MultiMarkdown Composer Beta (or Non-Sandboxed version) Stopped Running
As you may or may not have heard, Apple apparently let one of their security certificates expire, effectively breaking Apps downloaded from the App Store:
For most apps, this means either re-entering your App Store credentials in the dialog, or downloading a new copy of the application.
For the MultiMarkdown Composer beta, however, there is no way to automatically update. So there are a few steps to follow.
1) Delete the receipt file in your Library --
~/Library/Application Support/MultiMarkdown Composer/receipt. More information is here:
2) Delete the old copy of the App Store version of MultiMarkdown Composer, if it's still installed. You do not need to delete the beta or non-sandboxed copy. Empty the trash to be safe.
3) Download MultiMarkdown Composer 2.8 from the App Store again. Run that version at least once to ensure it works. Composer will install the new receipt automatically.
4) Now the beta or non-sandboxed versions should work again.
5) Once everything is working, you can delete the App Store version of Composer if you desire.
I'm sorry for any difficulty you have, but it appears that Apple's new certificate won't expire until 2035 or so. So at least this won't happen again for a long time....