Why won't Migration Assistant recognize my old Time Machine backup?
Seems that many people have difficulty restoring from a backup of a case-sensitive installation to a case-insensitive one.  Please see comments for some discussion and various ideas.

A work-around which seemed to be successful in this case: copy the data you need manually from the backups, using the Finder. (I wouldn't expect to be able to recreate the entire machine with all settings etc this way, but documents should be easy to restore this way, and perhaps even your entire home directory.)