Hi:
Yes. The problem should be in the 2 GB RAM limitation on 32-bit OS. However, I have not seen any problem in incorrect results due to the RAM is approaching the 2 GB limit. IE3D is using double precision for the matrix. It is good enough for ten's of thousand unknowns for antenna problems. All MOM matrices have a singularity at DC. In fact, all full-wave EM simulation algorithms have such a singularity. For some low frequency applicaitons, all of them will diverge at some point when the frequency is low enough. However, such situation should not happen in antennas.
For us, we have solved some problems with 19000 unknknowns requiring 2.6 GB on a Win64 machine and the results are good. Some user solved some problem using 8 GB RAM and they got good results. Certainly, we also solve some antenna array problem with 65K unknowns using iterative matrix solvers. Iterative matrix solvers are supposed to be able to yield high accuracy results for very big strucutre as long as the iterative procedure converges.
If you want to verify the accuracy with increased meshing density on IE3D, you have to use bull-force and use the standard SMSi solver or use the GEMS or AIMS iterative matrix solvers. You should try to go for 64-bit with more RAM. If you want to solve very big structuers with possible reduction in accuracy, there are other ways. Regards.