Does this happen when there are a huge amount of units in the game?
As you say, the game will become unresponsive when there are too many of them on the map-sound and music will still work and you can select units, but most if not all of them won't follow new orders (air is generally an exception even in that situation).
If that's your issue, I can only recommend lowering the unit cap; that said, it's entirely possible that those errors might point to another problem altogether.
