[imp] IMP 3.1 Horde 2.1 IIS 5.0 is working but the web server stop

[arn at scs-net.org]

Hello,

I've installed IMP on a Windows 2000 server with IIS (no choice, it's the 
customer system).

My configuration
IIS 5.0 
Windows 2000 Service Pack 3
PHP 4.4 last developpement version for today
Horde 2.1 (last stable version)
Imp 3.1 (last stable version)
My Sql 3.23.53-max-nt
Dual processor (heard there can be problems with PHP ? )
Connection to an IMAP server UW-IMAP(UNIX, this one)

Everything is working well, except that around once a day, the Web server will 
freeze needing a restart.
This webmail is used for an ISP and is under great load (around 10 000 
connection per day).

Do you have an Idea where I can find the cause of the freezing ?
No message in the events log (php should log there)
No message in the horde log

When the server freeze, it will use 70 % of the CPU, whereas it usually use 11%.

Thanks for any help, becaus I like this webmail and would like to keep it
Regards
Armelle Nedelec
Consultant
Jezz-Net Lebanon