Stripped thread

As in title, I've made a mess.

I was refitting the sumpguard before going to supper, just after changing oil&filter, and while tightening the rear bolt (the one under the engine) I've stripped the thread. I think it already was at a good point by itself because I haven't forced it too much. Anyway, I don't know exactly which thread has gone between the one on the bolt and the one on the welded metal tab, but I guess the one on the bolt has because it doesn't want to come out (if the metal tab's thread had been stripped instead, the bolt should come out quite easily, or at least I think so).
And this is the problem, because if I'll be able to find a way to take that @#* bolt out I could easily re-thread the hole, if damaged, or simply replace the bolt. I've already tried by turning the bolt with a spanner, while pushing it out through the hole in the sumpguard, but nothing has happened.
The curious thing is that I didn't want to remove the sumpguard either, but I did because a little amount of oil dripped inside it and I wanted to clean ...

Every suggestion is appreciated.

Simone

Ich verstehe nicht, Chrille! Könnten Sie bitte erklären?

Anyway, I've solved! And I'm very happy about it
I've put some more force in pushing down the bolt while turning it, and it came out.
Here's a pic of the three bolts:

[Blockierte Grafik: http://img709.imageshack.us/img709/615/75121757.th.jpg]

The one on the right is the one that drove me mad. As you can see, the one in the middle was beginning to get stripped, too. There was only one good out of three - the one on the left.
As the bolt didn't come out easily, I've re-thread the metal tab with an M6 tap to straight every possible metal burr, and since I was there I've re-threaded the other 2 tabs, too
Then three new bolts and washers, job done. Evvai!

Thanks for answering! Cheers!

Simone

I forgot: the screws I replaced the old ones with are made of zinc plated steel. Not sure about the material of original ones (does anyone know?) but I preferred to avoid installing stainless steel screws - if something wants to get stripped anyway, I prefer that a screws does, instead of its metal tab's nut

@Christian: figurati per il ritardo, nessun problema

Cheers! to all

Simone