Well, I downloaded the "unofficial official mods patch" and installed it correctly... But when I started oblivion the I HAVE NO GREETING. pops up on all npc's including kotn, except the shivering isles characters (the only ones unaffected by the patch.) and I have all dlc's except battlehorn. I set the load order as they stated in their instructions... I backed up oblivion still has the problem...
So I uninstalled it installed it again, still has the problem. I managed to fix the kotn though... but now I can't do the main quest or mages guild etc. any suggestions?

The most plausible cause I can think is something edited the common dialog (and is not one the DLCs) sometime ago. Just uninstalling the game and installing again isn't enough to fix some issues if it is present in the data folder and this folder wasn't properly 'cleaned' before the reinstall. At some extent the same applies to the C:\My documents.....\...\Oblivion folder, mainly the ini files and saved games.

I don't have an easier suggestion beyond reinstalling the game completely, from the DVD's setup app. Backing the /data and the /save (this one from the ..documents... directory) deleting them and only now, redoing the install. Test the game with a new created char. If all is fine, proceed installing the mods one by one. When done, try the saved games, returning one at a time. My advise is against trying to reuse the former /data albeit I have said to backup it, you bet.

Have you traveled through the SI portal? That bug is usually caused when you teleport from Tamriel to SI or vice versa without using the portal in Niben Bay.

Oh, how ironic... I do that alot, I'll try to fix that and see if it works
Never even knew that bug existed.


EDIT:
Son of a... Wait! can't say that... well, uh it worked, I guess i'll use system restore to renew my stuff again... well thank you very much!
so strange that a huge disaster happens from such a small cause...
thought I was losing my mind

For two times I opened the Edit windows to speak about something I saw once about the game 'thinking' the PC yet in Shivering Isles, but no simple way to say how (and because never happened to me) and you had already reinstalled the game prevented me to click the send

I too thank you Tchos, for the confirming information. A well earned kudos.