Actually, if you read the "Roadster" forum you will find many threads about tops that won't behave.

The most common culprit is the little micro-switch in the trunk that the divider activates.

What you describe is a new one to me. I've been here three years and I have not heard of tops that START to move, then fail. If you read thru the manual where it talks about the sequence of actoins that happen during raising and lowering, I think you will see why I think a limit switch somewhere is funky. But that is still just a guess. It COULD be the relays in the module that runs the pump motor.

Just very hard to diagnose this one from afar. It would be a challenge I'd take on.. but I"m in Georgia.