I'm told that FTM versions later than FTM16 include a feature that automatically synchs your genealogies (on your own computer) with what's on Ancestry.com if you subscribe to Ancestry?.
(This feature is in the "2012" version but may/may not have been in versions between it and FTM16. You can change the setting to "manual synch" in 2012.)
The synchronisation "feature" may require functions not available in IE before IE8(?), although I believe IE7 worked on our local addict's computer with FTM2012.
What appears to be corruption of your genealogy files may be a result of a "synch update" (?). Failure to import older files could be caused by them being "too far out of synch"(?) if the feature is turned on.
Versions of FTM prior to 2008 (FTM16 was the last of such?), when the program was "completely rewritten" may be unable to access some "features" now implemented by Ancestry, and/or changes in such features may have caused problems with older versions(?).
This is speculative - based on comments from my "resident consultant" - as I'm not a user (and certainly never inhaled).