As far as racking problems go, yes it is vital, repeat VITAL that the INS/IRS is fitted securely to the rack, but all such units have a central locking pin to ensure positive location with the rack, you should
never be able to get this wrong. If someone says to you that they've fixed inertial attitude errors by re-racking the unit, then it was never located correctly in the first place. (The rack alignment is set up during aircraft manufacture and this alignment is totally critical, and must never be altered
).
Dude 
Thanks Dude, I stand corrected on my terminology. Our two jets both came from the OEM with one of the three IRS racks aboard out of alignment. It was no small task to have this corrected by them. IIRC, they referred to the process as "re-racking." Musta just been an in-house term.
Best,
GC