problem with vTaskDelayUntil() stalling

I have a periodic task with plenty of stack. When I call  xLastWakeTime = xTaskGetTickCount();
TaskDelayUntil(&xLastWakeTime, /*LAMBDA_CTRL_RATE*/ 5); which should delay for  5 ticks, I never return from this call. Neither is any other task in the system contonuing to run. The platform is a LPC2138. Is there anything special I should think of to get this to work

problem with vTaskDelayUntil() stalling

I should mention that by using the debugger, it seems like the idle task continues to run, but nothing else ever happens.

problem with vTaskDelayUntil() stalling

Nevermind, I placed an ISR for another thing on #0 that was already configured for the tick timer.