[Zope] Problem submitting large files to the document library

Hi, has anyone ever had problems when submititng large pdf files to the Zope DocumentLibrary. I've got three pdf files to submit.. two of them are about 400K while the last is nearly 3M. The first two are loaded ok wheras I get an error when trying to submit the last large file... Is there anything I can do about this or do I simply have to resign myself to the fact that largish files are not supported? Cheers Ruth