Yes, thanks.

Looks like this portion of the JSON string is causing problems:
"quota":{"p":43,576431274414,"m":"44% von 512 MB"}

That comma in the percentage is not being caught by the JSON encoder.   
Does my fix work for you?

Changes have been made in CVS for this ticket:

http://cvs.horde.org/diff.php/dimp/imp.php?r1=1.233&r2=1.234&ty=u

This seems to happen only on my PHP 4 install.

If the messages are refreshed (Fetch Mails) I get errors like the following:

doActionComplete: SyntaxError-Badly formed JSON string: 
'/*-secure-{"response":{"poll":{"INBOX":4,"INBOX.horde.apps":3,"INBOX.horde.bugs":2,"INBOX.horde.cvs":1,"INBOX.horde.dev":0,"INBOX.horde.imp":0,"INBOX.Privat":0},"viewport":{"id":"**search_7t4ni6zo5t0kw8884ggsg","totalrows":10,"label":"Virtueller Posteingang","cacheid":"{mail.wg.de:143\\/imap\\/notls}**search_7t4ni6zo5t0kw8884ggsg","other":{"nothread":1,"sortby":0,"sortdir":1},"rowlist":{"183168INBOX":1,"183167INBOX":2,"183074INBOX":3,"182180INBOX":4,"56579INBOX.horde.apps":5,"56571INBOX.horde.apps":6,"56522INBOX.horde.apps":7,"33397INBOX.horde.bugs":8,"33382INBOX.horde.bugs":9,"76150INBOX.horde.cvs":10},"data":{"183168INBOX":{"imapuid":183168,"menutype":"message","rownum":1,"view":"INBOX","bg":["msgRow","unseen"],"size":"7 KB","date":"17:39:59","from":"Robert Brill","subject":"Heutzutage ist Impotenz ein Fremdwort"},"183167INBOX":{"imapuid":183167,"menutype":"message","rownum":2,"view":"INBOX","bg":["msgRow","unseen"],"size":"8 KB","date":"17:39:32","from":"Pisegna Thibodeaux","subject":"Shelter Workers Find 110 Parakeets In Seattlle Man\'s 1 Bedroom Apartment"},"76150INBOX.horde.cvs":{"imapuid":76150,"menutype":"message","rownum":10,"view":"INBOX.horde.cvs","bg":["msgRow","unseen"],"size":"4 KB","date":"17:38:25","from":"An: cvs@lists.horde.org","subject":"[cvs] commit: kronolith\\/lib\\/tests bug6031.phpt","listmsg":1}},"update":true,"request_id":null},"quota":{"p":43,576431274414,"m":"44% von 512 
MB"}}}*/'