Can't add new SimObjectPtr to GameConnection

My game requires that the user be able to control two objects simultaneously, the player and a GameBase object. But I'm getting stopped in my tracks fairly early on.

In GameConnection.h I added the following line after the declaration of mControlObject (I'm not in front of my dev machine right now, so forgive me if I make any capitilization or similar errors):

SimObjectPtr<GameBase> mControl2;

Then in gameConnection.cc I added the following in the GameConnection constructor

mControl2 =  NULL;

I've not exposed the variable to script, I've not assigned it a value anywhere, and I've not created any methods that use it. However, when I run the engine it crashes even before the GG splash screen is shown. It says the error is in netstringtable and reads "error ref count is already 0".

Any ideas why my additions would be causing this error. I did a search for SimObjectPtr and SimObjectPtr looking for similar problems, but came up empty handed. I also made the same changes on a clean build and had the same problem, so I don't think its anything I've done to the Engine.