EDIT: Apparently I have terrible luck. My Oblivion.ini file was corrupted not once but twice in a row from a fresh install. Going back through each step and deleting the INI file a second time seems to have fixed it. If anyone keeps on getting Error 5 just try deleting the Oblivion.ini file again.
The game crashes upon startup. When I try to use the default launcher the screen flashes black and then I'm back looking at my steam library. When I launch through Wrye Bash using the Launch Oblivion + OBSE 21.4 button I get Application Load Error 5:0000065434.
I have installed all the performance files and the 4GB Patch and I've tried Deleting Oblivion.exe and redownloading without the 4GB Patch to the same result. I tried unchecking all Mods including the DLC so only Oblivion was checked and it still gave the same message:
Please if anyone could offer any assistance that would be greatly appreciated!