[Zope] Commit_sub

Hello, I've got a big problem with uploading files. If the file size gets bigger(i.e. 1,8 MB), I got the nice 'attribute error:commit_sub'. I've followed the different threads but couldn't find any sollution. With a pdf-file with size about 60kb there is no problem! The files are added to a catalogaware zclass. Thanks for every hint.