Problem when trying to create a new user

Hi experts!!

I am working on EP 7.0 ABAP & JAVA stack, so the UME datasource is the R3_DATASOURCE.

When i try to create to create a new user from the portal i get the following message:

Current user has user creation permissions in the UME, but cannot create users in the back-end system (data source). The original and possibly untranslated message was: "No active writeable datasource found for user creation, check your Persistence Configuration.".

But i am actually able to create users to the ABAP client.

Any ideas???

Please help!!

Thank you in advance!!!