I experienced this also on someone's computer, when the person asked me for help to install Plus! because she couldn't....
The reason was something different (although SmileyCentral can also be the cause and you need to check that first, it wasn't in her case)....
The reason was the sponsor from Plus!
Explaination:
She once installed Plus! 2 with the sponsor, but Spybot S&D removed the adware from the sponsor (without she knowing about it, so I hadn't a clue either because she couldn't tell me).
Plus! was still running fine of course, but... whenever she (and I) wanted to install the new Plus! 3 it worked (the installation that is), but as soon as Messenger started to run and Plus! tried to hook, the same Recovery Window came up
.
Of course I had no clue that it was the sponsor, because the message doesn't mention it. It doesn't even mention a bad installation. Which in fact is correct though, because Plus! was installed correctly; only parts of the sponsor where removed, but still you couldn't install and run a new Plus! version over it.
Also, uninstalling Plus! didn't work because then a popup would appear with the message: "Plus! not installed properly, can't continue" or something.... (which seems also very strange and dodgy because I wanted to
uninstall it because I KNEW something was wrong, but it didn't let me
<- can this be fixed Patchou? I mean, why wont Plus! let me uninstall it, while I knew there is something wrong with it
)
Anyways, after much thinking and trying (and always getting the same errors), I gave it a shot in the dark and I decided to install Plus! with the sponsor and then trying to remove it again... And it finaly worked. So Plus! was uninstalled at last and then I could reinstall it without the sponsor with no problems....
In short & solution:
So, in short (but I hope Patchou read the above): it is also possible that you once had installed Plus! with the sponsor, but that the sponsor was removed by a program like ad-aware or SpyBot S&D. Whenever you want to update such a corrupted installation with the new Plus! 3 and without the sponsor, you will get the Recovery Window. To fix this (if this is the case), installe Plus! 3 WITH the sponsor, Remove Plus! 3, and reinstall without the sponsor....
/ 
