[imp] Unexpected logouts

[Jose-Marcio Martins da Cruz]

Hello,

I've just updated our horde installation :

Horde     3.1.6   ->  3.3.6
IMP       4.1.6   ->  4.3.6

and I'm having the following problem. From time to time, users which 
*are logged in* get logged out with this message in the web interface :

************************************************************
Login failed because your username or password was entered incorrectly.
************************************************************

At horde log file, I find this :

************************************************************
Mar 25 11:28:33 HORDE [error] [imp] FAILED LOGIN for joe [10.3.5.5] to 
{localhost.ensmp.fr:143 [imap/notls]} [pid 15562 on line
139 of "/export/htroot/htdocs/webmail/horde/imp/lib/Auth/imp.php"]
************************************************************

Any hint ? Or where or what kind of thing I should look for ? Not even 
sure if this is a horde or imp issue.

Thanks

José-marcio

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