% Processor time averaging around 90

Hi ,
We are deploying a new application to production. But while doing a load test with around 50 users , the % processor time counter increases very rapidly upto 95% and most of the users (around 30) fail during the load test. What could be the reason for this? I am running it on a SQL Server 2005 SP2 ,quad processor, win server 2k3 sp2 machine, and i have given all the server level settings to use all processors and boost sql server priority.There is not much blocking on the server and when i dig into the profiler trace no sql stmts are taking more time.Is there any other thing i need to look into to find out the bottleneck. any help will be appreciated
Thanks
Anna