Well I had deleted all objects in the scene except for 1 box with a displace modifier (for an outdoor heightmap) and 1 box with a texture - no other special modifiers and it just errored out.
Here is an example, a simple 3d studio max file that exports fine in 5.1 but does not in 5.2:
http://www.moocowz.net/SquishyError.rar
I also am very new to 3d modelling, so it is quite possible that I am doing something wrong and 5.1 just let it go by where as 5.2 doesn't.
Also, out of curiosity I tried creating a zone entirely in OZ5.2 following the help file tutorial step by step - and it always freezes when trying trying to use the ground editor. It never errored out, just hung there for hours at around 50% processor usage.