[Mike Betts]

Tom and Mike,

Assuming that you are using the competition templates, this could be a problem with your initialization (running in one direction) versus your main loop (reversing direction).

Exact cause could be different depending on your programming language choice.

I agree that posting your code is the fastest way for people to help.

You should also be sure that you have the correct firmware installed in your NXT brick and that the latest templates were used.

Regards,

Mike