I updated from Lion to ML DP4 a couple of weeks ago. No big issues until.... Yesterday I found a bunch of old mp3's on an external drive that I had forgotten about, so I imported them into my iTunes library. When iTunes Match kicked on and tried to do it's thing, I got this error message: I contacted Apple Support to open a case, but they were pretty clueless. I of course Googled the issue and found one "fix" that didn't work (hold Option key and turn off iTunes Match, then turn it back on). Are you guys successfully using iTunes Match with ML DP4? Any similar issues? Any ideas what the problem might be?