I'm having the same problem. I've used MB for years without this problem. As of Feb 12, Musicbee seems to crash regularly after about an half hour to an hour of use. Maybe less, but many times by leaving it in the background while doing something else, it has crashed. Crashed after I left it up after doing a Library scan and crash while I was in the middle of editing some tracks (I had MusicBee open at least 10-20 minutes prior. The only recurring variable I can tell so far is the amount of time MB is left up after being open.
I'm using Windows 7 Home Premium
I use Avira Home Security, Comodo Firewall, Malwarebytes 4.0.4, and SuperAntiSpyware.
I'm using the Blue > Midnight Skin
My Musicbee version is 3.3.7165 and my install hasn't changed much since I installed so I DOUBT any changes to MB is the culprit. I don't think MB is at fault here, its probably SOMETHING with the OS or some other conflicting software but I don't know what else.
Some other software I run often are Steam, Chrome, Corsar iCue, Windows Explorer, and Bionix Wallpaper Changer (but again, these have never been problems before)