I have been going nuts for the past three days trying to figure out why MB was crashing every time I tried to sync to my phone no matter what method I used. About 90% of my library is mp3 and about 10% are flacs that I encode on the fly to mp3 on sync. I very stupidly decided to change the file naming scheme on my phone so I was resyncing the entire library.
There was seemingly no pattern. I wound up doing it in batches, little by little. Sometimes it would crash at 5%, sometimes at 95%, but, every time, it would crash before finishing. Nothing in the error log because MB would just crash out. The only thing in the wifi sync error log were messages that it couldn't find the connection any more, which made sense because MB wasn't running any more.
After repeatedly restarting and adding more files, I finally got it down to only about 30 files to sync, all flac to MP3, and it would just crash on me immediately every time.
I should have known it was something to do with the FLACS, because that's the part of my method I'd changed recently (I didn't used to have FLACs in my library). Basic troubleshooting and logic that I should have employed THREE DAYS AGO. I ran a preview and sent the flacs that it showed it was going to try to sync through FLAC Frontend. As it turns out one (1) was bad. It was SWLABR by Cream. Stupid SWLABR caused me three days of misery.
So, if you encode on the fly and have this kind of problem, check the integrity of your files early, not after three days.
Hope this helps someone.