hi,
maybe you’ve found by now a solution but i often work in AE (pc) with mxf files and frequently After Effects won’t load them and crashes altogether.
i found that erasing completely this branch in the registry restores this functionality
HKEY_USERS\S-1-5-21-3063014461-3832367026-343455283-1000\Software\Adobe\After Effects\10.5
good luck!