Error importing SharePoint site collection - "there is an error during importing the Roles tag"

Hi, we are having trouble restoring a SharePoint 2010 site collection using our DPM 2012 installation. The recovery process goes fine (restore of the database, attach to the sql server, export into WFE's filesystem) and the last phase, the SharePoint import, seems to end with an exception. We see this in the WssCmdletsWrapperCurr.errlog file:

Caught Exception while trying to import Url .....
Exception message =
There is an error during importing the Roles tag
Exception Stack =
  at Microsoft.SharePoint.Deployment.ReadAttribute.String(....
....

It looks like it is a SharePoint import issue, but I'm not sure. We have tried to restore the site into an empty one, and the exception appears again, although it *seems*  that the content has been recovered. We have imported using the security info on the recovery point.

I've searched for that error message in the Net but I've been unable to find anything appropriate.

Do you have any hints?

Thanks.