Diablo II: LOD problem with mercenaries

My dad is playing single player D2:LOD and is having an issue with the mercenary. They’re not following him through the waypoints between Acts. I’m unable to find any solution (yet) through googling, so I’m hoping someone here knows what the problem may be.

The game has all the latest patches (I checked). He’s running on an Windows XP system. There are no mods or cheats installed.

Ideas, solutions, pointers?

Thanks!

Never mind. Dad had LOD installed but didn’t have the “Expansion Character” box selected when he created his character. She’s converted and the merc is playing puppy just like it’s supposed to.