Two points arising... well maybe three...
1 - Illori's last post says: "this is not going to cause your forum to break if it is not fixed right now
" - which is a relief. That's the main thing which was concerning me most, when I came across this problem (reported by the Administration Center when looking in the detailed view).
2 - Illori's earlier comment "it is not always best to upload files via ftp and run upgrade.php, this is why we have the package manager upgrades
" is all well and good, but it needs to be remembered that not everybody can
use the Package Manager successfully. In Windows, it's a nightmare (due to the differences in the permissions system) and it is neither simple to temporarily override the perms on an IIS-based environment, nor is it even a guarantee that the Package Manager will work even then! Thus, the manual-update-by-zip method is all that is realistically open to us, and of course, that's where this problem rears its ugly head. Presumably there's some kind of manifest which SMF relies upon to know which files are current, and for some reason, in the zip distro, this still thinks that Themes/default/PersonalMessage.template.php should be 2.0.2 (or rather, it thinks it knows that 2.0 is 'wrong', so barfs). This is presumably what's being fixed, I hope.
3 - I'd like to thank Illori for his help, but I would also really like to thank FinsandFur for his persistence! From reading this thread, it did look like he was banging his head against the wall for a fair bit until it was conceded that there is
a problem. I'm very grateful to him that wasn't the one who had to go through the headbanging myself!