Media Browser and Media Center cannot open file error playing movies

What fixed this for me was going into the Media Browser configuration tool and clicking advanced, and then cache. Clearing the items cache fixed the problem.

Also, depending on the types of files you are attempting to play it could be a codec issue. A good solution to this is the Shark007 codec pack. Here's a link for Windows 7. Scroll to the bottom and you will see the download link to 'Major Geeks'.

Media Browser - file cannot be found error when trying to play MKV files

Here is the solution to the problem I found:
1) Install this Divx Codec Plus pack
2) Install AC3Filter

Now my MKV files play and I can hear them. Without the AC3Filter I had no audio. I am getting choppy playback though so I don't know where to point the finger for that problem. Is it my network or is it a codec issue?

Movie Backdrops cleanup tool (for use with Media Browser)

I made a tool with the help of BAS Concepts that allows one to view all their backdrops, delete the one's they do not want, and have them auto renamed so they cycle properly in Media Browser. Check it out if you have been looking for a tool like this. It can be downloaded here.