that wouldn't lead to checkpages faults, which appear when processes trap on bad addresses.

i'd suspect an inconsistency between the source (eg, paging or lock data structures) and existing object files.

It could be that some other structure has changed (for instance Block acquired a magic value a few months ago).

Ordinarily I'd expect that to be caught by the -T compilation option and loader checks, but perhaps those aren't on by default.