Sorry, I thought you were saying it was working in AE and not mocha, and didn’t realize it was working yesterday in mocha and not today. I have a “canned” response because it is literally the most common answer to the issue and I find many users don’t look up supported formats. I am glad you search the forums. :)
However, if your issue is suddenly appearing, that is weird. Did you update your OS, codecs, or quictime lately? Did something change on your machine that we can use to narrow down the issue? What OS are you on? Why are you relinking the media? Could it be that if they are not on your hard drive you are having a networking error?
Let me know and we will try to track this down.