Small update - if I put things back *exactly* as they were it rebuilds the files correctly again... What I'm trying to do is convert my daily archive template (with only one post per day) to an individual template.  All my attempts have generated the error above.  Any tips?

I've started getting a strange error after I cut my date based template and tried using it as an Individual template.  Everything was working fine until I did that - and now, I still get the following error even if I put everything back as it was:

MT::App::CMS=HASH(0x82dc734) Use of uninitialized value at lib/MT.pm line 204.

I'm running Movable Type 1.4 incidentally (can't yet afford MT2.0 sorry.)  Any advice how I can fix this?

Well, now that I've RTFM...  Everything is working fine now, I had to rip out the MTEntries tags I had and change them to ArchiveNext, ArchiveLink etc tags to EntryNext, EntryLink etc.  I really should have read that manual more closely before posting, sorry to waste everyone's time.