Unfortunately, I have no idea, when or how this started, because I haven't used rsop in a while: while this file server (2008 R2 SP1) is in excellent condition (event logs clean, no other problems), it is not able to display rsop data.
rsop.msc fails with the error message "invalid data", while gpresult /h %temp%\result.htm fails with "access denied" - please note that this command was launched from an elevated command prompt.
Note: the gpupdate is possible and succeeds.
Monitoring with procmon, I see no access denials at all, so I have no clue, what is going on.
Only tried sfc /scannow - no inconsistencies found.
Googled - found literally no one with this very problem.
Tried rsop from the server GPMC - same error.
Had a look at wmimgmt.msc ->properties - security - rsop and subfolders: all seems normal.