Community Tip - You can change your system assigned username to something more personal in your community settings.
I am using Creo Parametric - Release 4.0 (connected) Release 4.0 and DatecodeM100Appearances menu is greyed out
Please provide a screenshot of your issue.
We really need more information.
With the information provided, the only possibility I can think of is the part or assembly is "locked" in the workspace so changes are not allowed/permitted.