I am receiving "an internal server error has occurred" 933150784 when conducting performance testing. This only occurs when the number of users is above 300. No errors if under that amount. Any ideas on what the problem could be?
You won't be able to get any help unless you've followed the rules. 000335652 states:
Performance tests must be submitted for approval at least two weeks in advance of the testing date(s), requests without a two week notice may be denied. To submit the request, navigate to the Help portal and select Network and Performance > Notify Salesforce of an upcoming activity > Schedule a Performance Test.
You are responsible for submitting tests ahead of time so that Salesforce can help monitor the tests and provide support.
Also, note that performance testing is only allowed in Sandboxes, and only with prior approval. If you are testing in Production, it may be that you've tripped over one or more resource limiters. Continuing to do so may result in sanctions or termination of your subscription.
Cease your testing now, and follow the appropriate procedures.