[Phanx]

Well, essentially you're looking for any lines that mention variables that aren't variables created by addons. Ignore the "global variable tained" lines for now. Once you find an interesting line, work your way back toward the top of the log through any/all of the "global variable tainted" lines mentioning the same variable, to see which addon(s) actually caused the taint. From there, it may or may not be obvious what the problem is and how to solve it.

However, if you can narrow down which addon is causing the problem, you should absolutely do that before you wade through 100mb of taint logs to see how it's causing the problem. Try to identify when the in-game error appears, and find a way to reproduce those conditions. For example, if the error always happens when you open your bags in combat, you can easily test it at a training dummy. Disable half your addons and go test. If the error doesn't appear, disable those addons, enable the other half, and test again. If the error does appear, disable half the enabled addons and test again. Continue this process until you narrow it down to a single addon.

Edit:
If you post your taint.log file here, someone might be willing to look at it for you, but that someone won't be me, sorry.