The Mail-box Enable process is stuck at "Initializing".
"Waiting for attribute to propogate" message in the temporary log file (stored in %temp% on the migration machine) and keeps repeating. Process never errors out or completes.
The OU where the target user resides may have an invalid character in it i.e * or >
Move the target user to a different OU and retry the Mailbox-Enable process to verify that this was the issue.