Throw your simulator in the bin, and start using your head. It is better.
I have seen more gray/lost hair resulting from staring at the ICE/simulator than most other things. The ICE/simulator is a great help in resolving 'clerical' mistakes, but not a means of resolving 'systematic' mistakes. If your design is right and you happened to make a register do 'double duty' the ICE is a wonder, if your design is wrong it is the bane.

Go through your code on paper, then use the ICE to see if what you expect (the notes on the paper) is happening, if not go back to the paper and figure out why not.

The way to debug is to be very systematic, not to throw another line in and see what happens.

Erik