Have you checked your mysql log for errors? Check what your max_allowed_packet variable is set to in the mysql config. If you're uploading 8MB files, it should be AT LEAST that.
no clues in the log files. I have max_allowed_packet=64M and I can put big blobs from my own hibernate-based app to the same db.
Note that the limit is 8k, not 8M, and the blob is still say 15k but everything above the 8k limit is zero.
as I replied to: http://www.jboss.com/index.html?module=bb&op=viewtopic&t=73336
The possible issue could be to weak sql column type for stroring blobs in schema created by hibernate.
Look at "slide_version_content" table and "content" column.
If you are using mysql and it's "BLOB" type it will store data up to 64K only.
Try altering column type with:
ALTER TABLE slide_version_content CHANGE content content longblob
(this is mysql specific command)
Could you try this and tell us if this was the issue?
Did the change of column type to longblob but that did not solve the problem.