Hello again,
I´m desperate because every new savegame that I make seems to be corrupted. I´ve tried to load a working save with the specs at minimun and the shader at static lightning but to no avail.
Once I got out of the problem by going out, doing a bunch of missions and then saving but latter those savegames got corrupted again.
Is there anyway out of this problem?

Are you running it as administrator?! - I know some people had that problem with the retail edition, not sure about the GOG version.

My user is in the admin group, but I´m not using the run as admin feature.
Also, the exact error is :
0023:05310491 xrGame.dll, CDialogHolder::CDialogHolder()
0023:00417183 xrEngine.exe, CBoneInstance::construct()
0023:05588544 xrGame.dll, CDialogHolder::`vftable'()
0023:056185F4 xrGame.dll
If its of any help, I´m using the Complete mod

I'd try reinstalling the game (make sure you run / install as admin this time) and see if that helps.

Edit: oh, yeah the CoP complete mod is not done by the same people as the others I think - and as I remember it created more problems than it fixed (might be wrong on that). I'd uninstall the mod.

That would mean that I need to start the game from zero again, as the savegames are not compatible

already tested that and I´ve checked that the flag is already on

Well, unless anyone else here comes up with a fix, you have two options:
1: get rid of the mod and restart the game (best to play vanilla the first time anyway).
2): post on the moddb page and see if anyone there has experienced the same / can help further.

Sorry I can't be of anymore help.

Ok, found it.
You where actually right, the whole issue was the 3Gb crash after all.
When you download the files for the fix and run them there´s the option to see if the flag is already on. I used that and saw that it was, so I discarted the problem beign caused by this, but I was wrong.
Even if the fix says that the file can already access more than 2Gb of memory you should patch it anyway.

So, here comes the guide for whoever runs with this problem again.
-Go to your install folder\bin and make a copy of xrEngine.exe, just in case.
-Download the 3Gb patch from http://www.moddb.com/mods/call-of-pripyat-complete and unzip it to a temporary folder.
-Copy the xrEngine.exe file to the temporary folder and change its name to Stalker-COP.exe
-Run START.bat and choose option (A) add.
-Copy the file to the install folder\bin and change its name back to xrEngine.exe
-Have fun!

Ah nice one! :)