NamedPipe-why they cause collision when serve an multi-processes client?

I am working on a Web based software on NT 4.0 and i built a NT service that use named pipe to communicate with multi-CGI process. But sometimes the server can't feel the client's connention when more than one client connect the pipe simultenously, only one client is served, other client also can connect to the pipe and can write a commend to it but the server thead don't know about it, so the client can't get anything untill read timeout.
I copied code from a MSDN article:Writing Windows NT Server Applications in MFC using IO completion Port (author: Ruediger Asche). I've been blocked here for days and I also writing another version without using IOCP, but things are same.
Please, if you know something about this or you know some reference of windows NT nimed pipe, give me an advise. Anything may help me. Thanks!