[GeoNetwork-users] Import XML limitation

Hi all,
I have installed Geonetwork recently but I could import only 2 metadata in Geonetwork .
At the third, I have this error : "Immediate unique constraint violation (_ANONYMOUS_CONSTRAINT_8) Columns = ( uuid ) Table = ( APP.Metadata )"
What's the problem ?

Thanks
Romain M
Sorry for my english..