[dev] IMP authentication timeout

[Luís Fernando]

after installing Horde 3.1.4 with IMP 4.1.4 and, everytime I try to
log to it, I get stuck on /horde/imp/redirect.php with this error message (code 500)
I'm using IMP as the authentication method

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Server Error
The following error occurred:

[code=SERVER_RESPONSE_CLOSE] The server closed the connection while reading the response. Contact your system administrator.
Please contact the administrator.
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After debuging it, I found the problem to be on:
/horde/imp/lib/Auth/imp.php (line 121):
return parent::authenticate($userID, $credentials, $login);

I can't debug more than that, but what I noticed that:
1) changing parent:: to Auth:: didn't change anything
2) putting a `echo a >>/tmp/test` right on the start of the function
authenticate, "a" is written just once (even with this second call)

any ideas/hints?

thanks,
Luis Fernando