svnadmin dump warning

From the below dump output, can anyone explain what kind of Œdataš is
referenced in a previous revision? Is it user data, Subversion data, etc?

Thanks,

Johnathan

-------------------------------------------------

* Dumped revision 13670.
* Dumped revision 13671.
* Dumped revision 13672.
* Dumped revision 13673.
* Dumped revision 13674.
WARNING: Referencing data in revision 13669, which is older than the oldest
WARNING: dumped revision (13670). Loading this dump into an empty
repository
WARNING: will fail.
* Dumped revision 13675.
* Dumped revision 13676.
* Dumped revision 13677.
* Dumped revision 13678.
Received on Tue May 2 17:40:20 2006