mapscript concurent access

[Stéphane RIFF]

Hello

I have an application thet serve map over internet :
   mapserver 4.4.2, mapscript, postgis + rasters

I think there is some problem occur when there are more than one user 
connected to the server.
I can't see error in mapserver log nor in php log.
Those errors occurs only when accessing postgis.
All the application is write in mapscript without use mapserv.exe.

Does somebody know bugs about that ???

Thanks