For me it is not just the federal withholding it is all taxes quit calculating properly. Federal and state withholding went to zero and social security and medicare also went to zero. I had to manually calculate those and override the amounts Quickbooks was calculating.

This problem was on six out of thirty employees and none of them new set ups. 

Also, it happened after an update. Maybe it's time to stop making excuses and look into the issue so that it may be resolved? Especially since quarterlies are coming soon and we need to be able to trust that our software is accurate.