Windows build crashes Unity after buying Unity Pro?!

I’m using Unity 4.6 , been developing my game for almost 2 years with Unity Free, I took the plunge and got Unity Pro, now the Build on Windows Desktop crashes (Fatal Error" Could not allocate memory: System out of memory! trying to allocate:…), seems like a out of memory issue… only once scene, I tried to disable all objects but that did not help.

The thing is though it built fine in the exact same version of Unity, just the Free version.
What could cause this?

The offending level plays fine in the Editor!
I cannot go to Unity 5, then I’d have to rework all of my physics so currently that is not an option sadly and I’m about to release my game on Steam!

Any help would be appreciated on what might cause this.

Fixed this by changing the build order of my scenes, seems that helps with memory management.