I am relatively new to AVID but the other day I got this error and since it was hard to find the solution online I decided to share what I did in case it is useful to you.
The error I got everytime I opened AVID was something like:
"Disk IO error occurred validating the media directory"
Then most of my media in my projects would be offline.
What I think created the problem (not an expert, just my theory)
I was trying to import a lot of files the night before, like 1300 .mov. And I was importing them from the same external drive in which it was saving the MFXs file. I am not sure if the amount of files, or the fact that it was taking info and saving info in the same disc corrupted something, or since it were many files it does not save the database until it finishes. In the end I think the database of my folder MFX/2 was corrupted (I am working in a big project and AVID created 2 folders automatically for me after some time).
What I tried
I went to the folder with troubles, MFX/2 and deleted the database: msmMMOB.mdb and msmFMID.mpr
Try starting avid again but with no luck. My hope was that AVID would regenerate the database after I had deleted it, and although I did scan the files this time, for some reason it did not save it.
Then I deleted the files that I had imported last night, which I think created the problem, first from the bin, then the actual bin, then deleted the MFX files in the folder (after closing AVID).
What solved it
Since I had another folder with a healthy database MFX/1, I decided to move all the MFX from folder 2 to folder 1. Then I restarted AVID and it scanned all the new files again, adding them to the database of folder 1.
Now it all works fine. Again, I am rather new at AVID, so I apologies if a more expert user reads this and thinks something does't sound good, or I used a term incorrectly. Please add your feedback to this, to help others.
I just decided to share this since I could not find an answer myself yesterday.