At the risk of being unhelpful, this one should be pretty straightforward to find and it's important to learn how to debug these.
Start with the error itself
Quote:
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ERROR Unhandled exception: edu.wpi.first.wpilibj.util.AllocationException: PWM channel 0 is already allocated
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Then look towards the end of the call chain (the text after the error I quoted) to figure out where in the code the error is happening. That should help you figure out what's going on. If you can't figure it out, let us know and I or someone else can help more (I did find the error in the code).