Possible fix for many errors. Don't use a Mac.
 

I don't know if this will help anyone, or if it even applies to you, but you should NOT us a Macintosh computer to download/upload/install any vBulletin software/hacks/mods.

I learned this lesson years ago. I saw several people having trouble with the "Cannot modify header information" errors when upgrading ibProArcade. As a test, and to verify my suspicion, I updated my arcade using my Mac and received these same errors after the upgrade.

When redownloading ibProArcade 2.6.7, unzipping, reuploading the files, even upgrading the product xml file, with my Windows XP computer. The errors no longer appear.

If you're a Mac user like I am, you can save yourself a lot of trouble by using a Windows computer to install/upgrade your vBulletin software/hacks/mods.

I hope this helps someone.