Here are the possible solutions, in approximate order of recommendation:
1. Install AL, avoiding all the engine-detection corner cases.
2. Remove MGS.
3. Handpatch this particular hack by deleting Node 5 in the 0x04E1 BHAV using the "Pescado's Delete" button in SimPE to bypass the problem in this particular hack.
Re Step 3: I now have the SimPE but I can't find this mysteriously quoted button. Also, where is the thing I need to delete? I understand how it works, and saw some other BHAV thingies in the program files, but I don't even know where to start looking in the thousands of files. Any help would be much appreciated.