Solution for the Exchange 2010 DAG "Source-Side 0xfffffae7 Error"

This is a fix for a  "a log file missing on the active copy" or a "source-side 0xfffffae7" error when adding a database copy across a DAG. The copy will error out and then go into a Failed or Suspended State.
I had this happen on all 20 of my databases after a failover, even though they had been healthy for months :(

What DID NOT work:

I tried running these commands several times (which are all over other forum posts and blogs) to no avail:

Suspend-MailboxDatabaseCopy -Identity "Server Name\Database Name"
Update-MailboxDatabaseCopy -Identity "Server Name\Database Name" -DeleteExistingFiles

I also tried to remove the DumpsterInfo registry key mentioned in other posts.

The DB's just kept going back to the Failed state after every seed attempt.

What DID work:

In order for the databases to seed correctly, I had to:

1. Dismount each database (I of course did this in off-hours).

2. Create new Temporary Folders for the Transaction Logs of each database (in my case I had 20 new temp folders to create).
  
- For instance, if you have a "DB1" with a "Log1" folder, create a "Log1Temp" folder and move the logs from "Log1" to the "Log1Temp" folder.

3. Then move (cut/paste) the Transaction Logs to the corresponding new Temp Folders.

4. Then Remount each database, which creates new clean logs in the original Log Folders.

After that, they all seeded correctly.

Once they are seeded correctly (and you're sure that you don't need the old logs anymore), you can Delete the Temporary Log Folders you created.
I had plenty of disk space so I waited until all DB's seeded to delete the temp folders, but if you're limited you can delete the corresponding folder after each one seeds.