timer proc problem


we are writing one application for digi em/wiem boards. Which has multiple threads. We have one polling thread which will send some poll messages to a remote server once every 10 seconds.The priority of that thread is 30.The application is working fine for some time but if we run the application for more than 12 hours, then the control is going to thread scheduler and after that its not returning back to the polling thread. When we connect the RAVEN debugger and see the stack call back then its getting some where in timer_proc function and its not returning back to the application poll thread.
Can any one tell what is the exact problem like whether it is the problem with the thread priority or with the scheduler itself

thanks in advance