OK, bit of a long shot but anyone have any ideas as to why a progam that was working perfectly one minute would then suddenly refuse to work (even it's setup files, so it can't even be reinstalled) in the space of one system reboot?
It's not virus/spyware, etc., related that's for sure. I've checked the PC, it's clean. The program in question (a dictionary) just suddenly stopped working. I haven't installed anything new, no new updates as far as I know either.
I've managed to install it on the Windows7 partition and it's working perfectly. It just no longer wants to work on the Windows XP Pro partition. Sadly I can't just switch to Win7 as the program I use it with cannot be installed on Win7 at present (mainly because I don't have the install CD with me).
Right now I'm just curious as to why this would suddenly happen =/

Maybe some other program (even the antivirus/anti-spyware one) messed it up? Given that it runs fine on Win7, it seems the problem is in the WinXP system's configuration.
I'd advise running a registry cleaning/fixing program; maybe there are some entries regarding this program that prevent it from being reinstalled (because the setup thinks it's still there).
EDIT: Or, you could first check the registry for entries about this particular software manually.

maybe run a memory testing program

^This^
could be a good idea as well; indeed, "address" implies memory. It'd be strange if your memory failed while you rebooted your system and it didn't give any other sign of it, and also, it'd have problems under Win7 as well, but it might worth a try.

See if you can install it in Safe Mode. If you can then it'll be a windows config issue & you can selectively disable components until you figure out what the issue is

No dice in safe mode. That was the first thing I tried. There's also nothing in the registry. Trying to run any of the exes related to that program (including its setup.exe) simply returns that error.
I doubt it's a ram problem as surely that wouldn't just affect one program? But if anyone can suggest which program to use to test the ram that'd help.

memtest86. It comes on the liveCD of most distros of linux & there's a few places to download it seperately.
Frankly by the sound of the issue and the fact it works on the same physical machine but a different OS I'd eliminate ram as the problem.
Weird thought, have you tried copying it to a different section of the HDD to run it?

Sadly it's a very finicky program. It *has* to run from it's specific default location, else it won't run correctly. And it's already in the default location.
I'm thinking I may just have to reinstall virtual PC so I can run it in Win98 (I think it was originally meant to run under the 95/98 builds of Windows).
Oh and even running the installer from the CD gives the same error, so I expect even that won't work.
I expect I could do an entire reformat but that's something I can't do right now as again, necessary install disks are not available here. And besides that, I really don't want to go through the resulting DRM mess right now. I'd rather do that when I get a Win7 once it's released.

wouldn't just giving in & using http://dictionary.cambridge.org/ work better at this point?

Only if they carry technical Japanese U_U

Do you have Comodo Firewall installed?
I had a similar problem when accessing my old accounting software a few days ago.
After trying a few things I remembered that Comodo had automatically updated itself the day before.
I uninstalled Comodo and everything worked fine.
It seems their new automatic update doesn't play well with 16-bit software.
Hope this helps,
TheBrownDragon

Yes I do. And I'm starting to think that you may be right. As it's working on the old PC for which I haven't updated Comodo. It works on Win7 for which I haven't updated Comodo. And it works on the virtual install of win XP pro I just made (which has no firewall, etc. installed at all). Both Win7 and the old PC are set to prompt me for Comodo updates, but I'm not sure if this PC is doing so as I turned off some of the notifications as they were annoying the hell out of me (mainly virus definition update notices which would pop up several at a go).
Also thinking back, I think I had a similar issue with Penumbra when trying to update that last week. The exe lost it's icon (which I notice now, so has this program) and it could not be accessed. I had to go into Win7 to delete it and redownload from Steam. I've since told Comodo to stay away from my games.
However, I find no entries in any of the Comodo rulesets for this dictionary program. So I guess I may have to try uninstalling and reinstalling Comodo then adding exclusions before trying to install again.

Thanks for that, I'll give it a try later tonight and see what happens (although I've now deleted the program from this OS, I can see if the installer will at least work =) And thanks for finding that workaround, I did have a look on their forums, but I find the place so confusing that I can't find anything on there.

Renaming that DLL worked. Cheers.