32bit and 64bit compatibility

I'm helping a friend with some VBA work on a Excel spreadsheet. My Office is 64bit and his are 32bit. For some unknown reason the sheet doesn't want to run on his 32bit anymore:sick: The error message is something about not enough resources available. It works fine on my 64bit Office. His laptop has a much higher spec than mine so computer resources should not be a problem.

The error is shown on a line where we call a function of Excel with Application.WorksheetFunction.XIRR(...)

Does anyone know if there are compatibility issues between 32bit and 64bit Office? The spreadsheet itself is currently 250MB in size. Could this be an issue?