After migrating AD from 2003 to 2012, I ran into this issue on a RADIUS server running 2008 R2, used for authentication. When attempting to retrieve AD information for a particular user, the following error appeared:
An error (1301) occurred while enumerating the groups. The group's SID could not be resolved.
The solution (at least for Windows 7 and 2008 R2), is to install hotfix 2830145.
The hotfix is only available by request through e-mail.
When attempting to log on to a 2012-based domain controller, the following SIDs are unmappable:
Installation of Windows 7/2008 R2 Service Pack may fail with error 0x800f0a12 if access to the BCD was denied during installation, which is required during the installation of the service pack. This can occur if the volume automount policy was set to disabled, or, in rarer cases, if the BCD database is corrupt or missing, or if something is wrong with the boot partition (where the bootloader lives).
Open an elevated command prompt, and run DISKPART.
Enable the automount policy:
DISKPART> automount enable
Restart the server, and try installing the service pack again.
If the above did not resolve the issue, there may be a problem with the boot partition.