You could also try the following but you do need to have full control set in your user privleges
1.) Close all DGN files
2.) Bring up the dos prompt and change directory ("cd") to the following location (may be slightly different on your computer):
cd C:\Program Files (x86)\Common Files\Bentley Shared\GEOPAK\
3.) Key-In "REGSVR32 BentleyControls.ocx" and press Enter.
You should get a message "DllRegistryServer in BentleyControls.ocx succeeded"
4.) Now exit the dos prompt, go back into your DGN file and try again