After 4 hours of googling and reading I give up..
I have a Ubunu server with my media on. My HTPC access this data using Samba. I just upgraded (with a clean install) from 6.10 to 8.04. The problem is that when I set up Samba again suddenly there seems to be a 4 GB file size limit when using the share. If a file is bigger than that the size is reported as smaller and I'm unable to use the file from any of the other computers in the network.
The file system on the disk is ext3 and the Samba version is Version 3.0.28a .