studio 5000 error when opening project

Someone sent me a acd file to look at for them and I am getting the following error when trying to open it in studio 5000:

cannot overwrite existing project file because its security information is either missing or is inaccessible

Any idea what this means? My first thought is they have incorporated some type of security into the acd file. Any thoughts?

What version of Studio 5000 are you running and what version is the file? You can open the .ACD as a text file, the first many lines will tell you revision history in plain text, the last instance will be it's current version.

yeah It looks like the file is corrupted, as I dont see of the plain text at the beginning.

I should mention that I opened it with Notepad++, not sure what Notepad would think about it.

edit: notepad displays it the same as ++

Solution that worked for me

Restart RSLogix, while holding CTRL & Shift until it has completed to restart completely

worked for me !

Knowledge Base # 512161 on Rockwell's site