The clue to this problem is here (taken from 
http://httpd.apache.org/docs/current/en/mod/mod_rewrite.html):

  This directive is required when you use a relative path in a 
substitution in per-directory (htaccess) context unless either of the 
following conditions are true:
     The original request, and the substitution, are underneath the 
DocumentRoot (as opposed to reachable by other means, such as Alias)...

My horde installation like the one reported previously are not 
physically located under document root but appears as such, using 
Alias directive. Rewrite module is enabled even though we don't use 
them in the server configuration. Nag would never accept, neither to 
create new task, nor to edit existing one. Though it could be done 
partially through kronolith. I must also mention that this horde 
production serveur has been up and running since more than three years 
passing from H3 to H4 and finally H5 whithout major problem except 
this one with H5.

Adding the following directive to the .htaccess file provided with H5 
which is located at the root directory of the horde installation, just 
after the line "RewriteEngine On" did solve the issue:
         RewriteBase /horde/

Adding the same directive in the directory section of the 
configuration file *does not* appear to work.

The .htaccess file, however seems to be a file that might be 
overwritten by future upgrades. May I suggest the Horde dev to at 
least include this information in the upgrade instructions for people 
having similar installation.

Please take this discussion to the mailing list.

Two I forgot: What's in the Apache access and error logs when you're 
accessing the page?

Regards,
Jens

Hi Steve,
I hate it too if I cannot see what's going on... so add these to your 
Apache configuration to see if any rewriting takes place at all:

       RewriteLog     /tmp/mod_rewrite.log
       RewriteLogLevel        2

You should see more than one line per incoming request in the log. And 
remember to deactivate once you're done - that log tends to grow.

Regards,
Jens

root@mail:/var/www/horde# updatedb
root@mail:/var/www/horde# locate mod_rewrite.so
/usr/lib/apache2/modules/mod_rewrite.so
root@mail:/var/www/horde# a2enmod rewrite
Module rewrite already enabled

And did you check that mod_rewrite is in fact enabled in your Apache 
configuration?

Thanks for the response mate,
however the issue remains this is my updated horde.conf in 
/etc/apache2/conf.d/

#####################################

Alias /autodiscover/autodiscover.xml /var/www/horde/rpc.php
Alias /Microsoft-Server-ActiveSync /var/www/horde/rpc.php

Alias /Autodiscover/Autodiscover.xml /var/www/horde/rpc.php
#Alias /autodiscover/autodiscover.xml /var/www/horde/rpc.php
Alias /AutoDiscover/AutoDiscover.xml /var/www/horde/rpc.php

Alias /horde /var/www/horde
Alias /webmail /var/www/horde

<Directory /var/www/horde>
            Options +FollowSymLinks
            AllowOverride All
            order allow,deny
            allow from all
            AddType application/x-httpd-php .php
            php_value include_path ".:/usr/share/php"
            php_value open_basedir "none"
            php_value upload_tmp_dir "/var/www/horde/phptmp/"
</Directory>

<IfModule mod_rewrite.c>
#  <IfModule mod_ssl.c>
     <Location /webmail>

#      SSLOptions +StrictRequire
#      SSLRequireSSL
#      SSLRequire %{HTTP_HOST} eq "www.swartsit.com"
#      ErrorDocument 403 https://www.swartsit.com/horde

       RewriteEngine on
       RewriteCond %{HTTPS} !^on$ [NC]
       RewriteRule . https://%{HTTP_HOST}%{REQUEST_URI}  [L]

     </Location>
#  </IfModule>
</IfModule>

#####################################

Again I have tried multiple things, commenting the lot or just some or 
nothing at all.

Can someone tell me where I could find logs on this?

This is what is in my .htaccess file for horde stored in /var/www/horde

#####################################

allow from all

<IfModule mod_rewrite.c>
     RewriteEngine On
     RewriteCond   %{REQUEST_FILENAME}  !-d
     RewriteCond   %{REQUEST_FILENAME}  !-f
     RewriteRule ^(.*)$ rampage.php [QSA,L]
</IfModule>

#####################################

Any help is greatly appreciated.
If you ever find yourself in Western Australia I will buy you a beer :)

Talk about incentive...

Regards,
Steve

Well, I'm not one of the devs, but you seem to lack the proper 
AllowOverride statement:
it ought to work with "AllowOverride All", but less may be sufficient, 
too. "None" will definitely not work, no matter what you do to enable 
Rewriting below. It's those rewriting rules that are overwritten in 
.htaccess...

Regards,
Jens

Ok I have made another bug ticket #11747 but it obviously is a 
duplicate. I apologize for that.

However trying to sift through the lists is a pain in the buttocks.

I realize that mod_rewrite must be enabled however this is my horde.conf

Alias /autodiscover/autodiscover.xml /var/www/horde/rpc.php
Alias /Microsoft-Server-ActiveSync /var/www/horde/rpc.php

Alias /Autodiscover/Autodiscover.xml /var/www/horde/rpc.php
#Alias /autodiscover/autodiscover.xml /var/www/horde/rpc.php
Alias /AutoDiscover/AutoDiscover.xml /var/www/horde/rpc.php

Alias /horde /var/www/horde
Alias /webmail /var/www/horde

<Directory /var/www/horde>
            Options +FollowSymLinks
            AllowOverride None
            order allow,deny
            allow from all
            AddType application/x-httpd-php .php
            php_value include_path ".:/usr/share/php"
            php_value open_basedir "none"
            php_value upload_tmp_dir "/var/www/horde/phptmp/"
</Directory>

#<IfModule mod_rewrite.c>
#  <IfModule mod_ssl.c>
#    <Location /webmail>
#
#      SSLOptions +StrictRequire
#      SSLRequireSSL
#      SSLRequire %{HTTP_HOST} eq "www.example.com"
#      ErrorDocument 403 https://www.example.com/horde
#
#      RewriteEngine on
#      RewriteCond %{HTTPS} !^on$ [NC]
#      RewriteRule . https://%{HTTP_HOST}%{REQUEST_URI}  [L]
#
#    </Location>
#  </IfModule>
#</IfModule>

I tried with the commented section and without, no luck.

Could the dev's please add some form of documentation for this?

Cheers guys,
Steve

Duplicate of a number of tickets and mailing list posts. You need to 
enable mod_rewrite. Search the lists for more info.

Devs: We should create a todo for removing  routes from Nag OR update 
the UPGRADING doc. Considering the number of reports, I vote the 
former. We could put back the functionality in Nag 4.1 or 5 if/when 
more of the apps might make use of routing.

When pressing "save" in the nag "create new task" form, I'm receiving 
a 404 page:

acces_log:
192.168.103.81 - - [21/Nov/2012:14:09:11 +0100] "POST 
/horde5/nag/t/save HTTP/1.1" 404 1449 
"http://***myserver***/horde5/nag/task.php?actionID=add_task&tasklist_id=***somelongid***" "Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20100101 
Firefox/16.0"

error_log:
[Wed Nov 21 14:09:11 2012] [error] [client 192.168.103.81] File does 
not exist: /srv/www/htdocs/horde5/nag/t, referer: 
http://***myserver***/horde5/nag/task.php?actionID=add_task&tasklist_id=***samelongid***

In bug #11727 the same result seems to happen, but I do have 
Horde_Routes installed:

horde/nag                        4.0.0       4.0.0 A web based task 
list manager
horde/Horde_Routes               2.0.1       2.0.1 Horde Routes URL 
mapping system

I'm working with Kolab integration, my task list is IMAP-based. I'm 
selecting my personal list, not someone else's. Except for the 
corresponding error message in Apache's error_log, no problem nor 
error is reported, i.e. in Horde's log.

How may I go about debugging the cause of this, any pointers, anyone?