ext3 can, and does have a file size limit. It depends on the block size it was created with. Though doubt this would be the case
As using 1KB block size results is a max file size of 16GB.
V3.5 of ReiserFS does have a 4GB file size limit, 3.6 is 8TB. XFS has a limit of 8EB, and JFS 4PB. NTFS is 16EB. Those are single file size limits.
Unless you're using ReiserFS 3.5, or did an ext3 format using a block size less than 1KB, I don't believe it's a file system issue.
Maybe check disk quota, fsck the drive, free space, or ulimit -a?
Also, are you mounting with CIFS? If not try that.