Merging termbases that won't open in MultiTerm Desktop

I've had so many 'bugs' with MultiTerm 2017 that I've ended up with 2-3 different termbases for the same fields (_NEW, _NEW NEW, etc.). I've decided it's about time I tried to merge these but when I try to open the old ones (which I can no longer add to) in MultiTerm 2017 Desktop (in the hope that I'll somehow be able to merge them) it tells me I can't as they were 'created with an unsupported version of MultiTerm', even though I've only ever had this version. I've contacted support and they were very unhelpful. I've also tried a few things people have suggested in the forums (renaming the MultiTerm and Studio folders) but to no avail.

Any idea what might help with this, or how I might be able to merge them without going through this stage (too much to hope for?).

Many TIA,

Vicky