Also, make sure that you DO NOT have any 25% fills as the surface fill of a material in any of the S/E windows.
I had a case where, after applying the 25% fill to a material and opening ONE section, I could not save the file and got the heap zone error. Changing the fill to a different one, and rebuilding the section, brought everything back to normal.
HTH,
Djordje
ArchiCAD since 4.55 ... 1995
HP Omen