Either way, there isn't a problem with the method call.

The sequence table maintained by MDB2 to keep track of primary keys is 
corrupted or just plain wrong. Did you change it by hand?

yes, after some troubleshooting I found the following error:
Nov 30 15:19:55 HORDE [error] [turba] DB Error: constraint violation: 
UPDATE horde_histories_seq SET id = LAST_INSERT_ID(id + 1) 
[nativecode=1062 ** Duplicate entry '3223' for key 'PRIMARY'] [pid 
23757 on line 198 of 
"/var/www/webmail/horde-webmail-1.2.4/lib/Horde/History.php"]

Which could be the cause?

So you're saying it works fine with a clean install, but doesn't work 
for your existing install? Same code versions?

I installed a brand new horde with a fresh db and seems this bug won't 
apply. So it could be a problem on sql of the horde installation.

Which can be the cause?

Peace,
R.

even with xmlrpc...

Peace, R

Do you know that this is specific to SOAP (as in the bug title)? Or 
have you tried other RPC backends?

horde webmail 3.3.5 / turba 2.3.2

getActionTimestamp always return 0. http trace follows

(Pdb) print 
server.contacts.getActionTimestamp("20091125212217.12527jgoulnhlpmh@newwebmail.eng.it","add")
*** Outgoing SOAP ******************************************************
<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope
   SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"
   xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/"
   xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance"
   xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
   xmlns:xsd="http://www.w3.org/1999/XMLSchema"
<SOAP-ENV:Body>
<ns1:contacts.getActionTimestamp xmlns:ns1="urn:horde" SOAP-ENC:root="1">
<v1 
xsi:type="xsd:string">20091125212217.12527jgoulnhlpmh@newwebmail.eng.it</v1>
<v2 xsi:type="xsd:string">add</v2>
</ns1:contacts.getActionTimestamp>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>
************************************************************************
*** Incoming SOAP ******************************************************
<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope 
xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" 
xmlns:ns1="urn:horde" xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/" 
SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"><SOAP-ENV:Body><ns1:contacts.getActionTimestampResponse><output 
xsi:type="xsd:int">0</output></ns1:contacts.getActionTimestampResponse></SOAP-ENV:Body></SOAP-ENV:Envelope>
************************************************************************