No mapping between account names and security IDs was done.
When trying to add a new group to role membership of an SSAS cube, I was presented with this error. The new group definitely existed and was spelt correctly. The problem was one of the existing users in the role that didn’t exist anymore.
It seems when adding new members to the role, SQL Server validates all the existing users as well. It was simply a matter of searching Active Directory for all the users and groups and seeing which one didn’t exist.
After removing that one I was able to add the new group with no problems.