Protect object from accidental deletion unchecked, full permission is given, all objects removed from OU.
Here is more specific error when I am trying to delete OU in ADSI Edit:
Operation failed. Error code: 0x20ce
The requested delete operation could not be performed.
000020CE: SvcErr: DSID-0315342B, problem 5003
(WILL_NOT_PERFORM), data 0