WaitForJobs() returns false

Hi.
Why can bool WaitForJobs(int jobCount, int timeOut) return false, if I am sure that there is at least one job waiting to be processed?
Is there any way to reach the error cause?

I am using Terminal Server Edition v.4.4.1
Same program in the free Stand Alone Edition v.4.4.1 works perfectly.

Thanks in advance for your help