Changes have been made in Git (FRAMEWORK_5_0):

commit a0a8760ae25bacc2321e1e5f7dd4f2cbb13126b2
Author: Michael M Slusarz <slusarz@horde.org>
Date:   Tue Jun 4 14:02:00 2013 -0600

     Bug #12291: Base element is a non-IMAP element

  imp/lib/Imap/Tree.php |    2 +-
  1 files changed, 1 insertions(+), 1 deletions(-)

http://git.horde.org/horde-git/-/commit/a0a8760ae25bacc2321e1e5f7dd4f2cbb13126b2

I've found what triggers the problem.
If I untick "Use IMAP mailbox subscriptions?" Then I get the IMAP 
errors. Users who used subscriptions were not affected.
I'm guessing that's the nav_poll_all variable you were talking about?

And the good news is that your patch fixed the problem :). Thank you.

*Still* can't reproduce, even with nav_poll_all on.  But if I manually 
insert the "base\0" entry into the poll list output, I can reproduce.

Not sure why this is causing issues on your server. But I'm not going 
to bother to trace either since the patch will fix.

Changes have been made in Git (master):

commit a2b2e38e69eda1a35b5b299c1fccefab93ac8da0
Author: Michael M Slusarz <slusarz@horde.org>
Date:   Mon Jun 3 15:24:00 2013 -0600

     Possible fix for #12291

  imp/lib/Imap/Tree.php |    2 +-
  1 files changed, 1 insertions(+), 1 deletions(-)

http://git.horde.org/horde-git/-/commit/a2b2e38e69eda1a35b5b299c1fccefab93ac8da0

For some reason do you have the nav_poll_all preference as true?

With that setting it seems the "binary data" is an invisible character

S: 5 OK List completed.
C: 6 LIST () "" ("INBOX" "INBOX/spam" ~{5+}
C:  "Drafts" "Junk" "Sent" "Trash") RETURN (STATUS (MESSAGES RECENT UNSEEN))
S: 6 BAD Error in IMAP command LIST: literal8 not allowed here
C: 7 LIST "" "INBOX" RETURN (STATUS (MESSAGES RECENT UNSEEN))
C: 8 LIST "" "INBOX/spam" RETURN (STATUS (MESSAGES RECENT UNSEEN))
S: base BAD Error in IMAP command "DRAFTS": Unknown command.
C: 14 LOGOUT
S: * LIST () "/" INBOX
S: * STATUS INBOX (MESSAGES 339 RECENT 0 UNSEEN 0)
S: 7 OK List completed.

This looks correct.
I have no idea where the entry between "INBOX/spam" and "Drafts" is 
coming from.  I don't see this, and I am using Dovecot 2.2.2 also.

You need to add 'debug_raw' => true to backends.local.php so I can see 
what those 5 bytes of extra data actually are.

Well done on the debugging output :)

Here is what I have:
S: * OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID 
ENABLE IDLE STARTTLS AUTH=PLAIN AUTH=LOGIN] Dovecot ready.
C: 1 STARTTLS
S: 1 OK Begin TLS negotiation now.
C: 2 [LOGIN Command - username: junkfood@addict.com]
S: 2 OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID 
ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS 
THREAD=ORDEREDSUBJECT MULTIAPPEND URL-PARTIAL CATENATE UNSELECT 
CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC 
ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS SPECIAL-USE 
BINARY MOVE COMPRESS=DEFLATE QUOTA ACL RIGHTS=texk] Logged in
C: 3 ENABLE QRESYNC
C: 4 NAMESPACE
S: * ENABLED QRESYNC
S: 3 OK Enabled.
S: * NAMESPACE (("" "/")) (("shared/" "/")) NIL
S: 4 OK Namespace completed.
C: 5 LIST () "" ("*" "shared/*")
S: * LIST () "/" INBOX/spam
S: * LIST () "/" Drafts
S: * LIST () "/" Sent
S: * LIST () "/" Trash
S: * LIST () "/" Junk
S: * LIST () "/" INBOX
S: 5 OK List completed.
C: 6 LIST () "" ("INBOX" "INBOX/spam" ~{5+}
C: [BINARY DATA: 5 bytes]
C:  "Drafts" "Junk" "Sent" "Trash") RETURN (STATUS (MESSAGES RECENT UNSEEN))
S: 6 BAD Error in IMAP command LIST: literal8 not allowed here
C: 7 LIST "" "INBOX" RETURN (STATUS (MESSAGES RECENT UNSEEN))
C: 8 LIST "" "INBOX/spam" RETURN (STATUS (MESSAGES RECENT UNSEEN))
S: base BAD Error in IMAP command "DRAFTS": Unknown command.
C: 14 LOGOUT
S: * LIST () "/" INBOX
S: * STATUS INBOX (MESSAGES 335 RECENT 0 UNSEEN 0)
S: 7 OK List completed.

IMAP log is needed.


To further debug this issue, we need details of the IMP -> IMAP/POP 
communication.

To enable debugging, see instructions contained in 
imp/config/backends.php (the 'debug' config parameter).

Debugging should not be enabled on a production server,   Attach/post 
only the portion of the log that directly deals with the problem 
reported (it may be simplest to clear the log file and then perform 
the event that causes the error).

The portal view crashes with an error 500.
It's coming from the mail widget.

Horde error:
ERR: HORDE [imp] IMAP error reported by server. Error in IMAP command 
LIST: literal8 not allowed here [pid 15147 on line 571 of 
"/webmail/imp/lib/Imap.php"

PHP error:
PHP Fatal error:  Call to undefined method stdClass::getCommand() in 
/usr/local/lib/php/Horde/Imap/Client/Exception/ServerResponse.php on 
line 74

The IMAP server is Dovecot 2.2.2