prescribed displacement with time dependant study

I am having trouble with my model, so now I have a really simple test file to find the problem.

There is a block and it moves 1mm with prescribed displacement during 0.1ms.

The results show me that there is high stress in the block even though it is a simple movement.

And the block moves all the way down to 1mm in 0.02ms (not in 0.1ms) , only stresses vary for the rest of the time.

How can the block evenly move during 0.1ms and how can I remove the strange stress?

I would appreciate any help.

Thanks,

Jay