I think rather a lot more detail would be very helpful!
First, exactly which version and variant of MEP? Then what are you attempting to do when the error message appears? What is the exact, full message? What format are your video files and to what format (presumably DVD) are you wishing to export them? Include any other information you think might be relevant!
I have never seen that message so a step by step method to recreate the problem might also prove very helpful.