Upgrade to SC2, the WC3 pathing system cannot cope with moving so many units for a single player at the same time. No I am not joking, WC3 really does not support moving a lot of units for a single player, unlike SC2 where there is no such limit next to how slow you want everyone to play at.
In WC3 you can work around this limit by removing collision from units so fewer micro-move orders are needed or by breaking the player into multiple players (like done in SWAT Aftermath) so that no player exceeds the limit. Simpler terrain can help since the less obstacles are encountered the longer micro-moves will last.
Symptoms of hitting the WC3 movement limit for a player are units standing around when ordered to move, units stop-starting when they move and units forming sort of chains when moving a group from one place to another.