[horde] Problem with session_start()

[lst_hoe02 at kwsoft.de]

Hello,

since recently we have a lot of the following in our logfile:

Dec 17 11:33:41 ftp HORDE: PHP ERROR: session_start(): The session id  
is too long or contains illegal characters, valid characters are a-z,  
A-Z, 0-9 and '-,' [pid 32572 on line 69 of  
"/usr/share/php/Horde/Session/Null.php"]

any idea what to fix to get this work?

Horde/IMP are all latest and PHP settings are mostly default.


Thanks

Andreas