We did a load test on the web application running on following server to determine the scalability and the following are the architecture

2 App server (running windows 2003 32 bit with websphere)
1 DB server (running win 2003 32 bit with db2 version 8.2)

The configuration of the DB2 db server is as follows

Processor: 8 cpu at dual core
Memory: 16 GB
Hard disk: 5 * 100 GB SCSI ( what is the bus bit and data rate, please mention the type of scsi)
Operating System: Windows 2003 32 bit

The DB Server scaled upto 300 users and then the DB2 Crashed and we got
the following information

1) Faulting application db2syscs.exe, version 8.1.15.254, faulting module db2sys.dll, version 8.1.15.254, fault address 0x00080d46.

2)The Open Procedure for service "DB2_NT_Performance" in DLL "D:\Program Files\IBM\SQLLIB\BIN\DB2Perf.DLL" failed. Performance data for this service will not be available. The Status code returned is the first DWORD in the attached data.

3) Win32 API : RegOpenKeyEx returned Access is denied.

There were severe disk issues in the earlier test and we were not able to determine what was causing this issue. What would be the possible cause for the crash as the DB2 box was a powerful IBM x3950 running on Windows.

The cause for the crash is a bug in DB2. Period. (The only exception would be if the DB2 executables and libraries got corrupted or if you run unfenced routines that are not properly working.)

So you may want to contact IBM support and open a PMR. That's the only way to get the issue resolved and fixed.