Combat Skills cease working

I have a Blessed Hammer paladin. Everything was proceeding as planned until, Hell/Act 4. All of a sudden, his Combat Skills cease working. His hammers and his Holy Shield disappear. It seems as if he is in a “time out”. After approximately sixty seconds, his Combat Skills return, and everything is back to normal.
This occurrence appears to be random. At times he can clear a whole level without interruption and the next level he will be interrupted two or three times.
Do you have an idea as to what the problem may be?