I was hanging around here to see MBWE hacks, then I saw your post. I experienced a similar problem approx. 3 years ago for a long time. My issue was freezing, too. However, MBWE used to freeze during large file transfer operations(either big files or large amount of files). My OS was Windows 7 Beta before this issue started. After installing Windows 7 Pro, the issue began.
I did look for solutions for a long time but it seemed nobody else was having a similar issue at that time. All I could guess was about Windows 7's secure networking stuff, like encryption.
For home network, I disabled new network encryption features of Windows 7 at that time because I didn't have this issue while transferring files from PCs without Windows 7. It did the trick for me. Related settings can be found under Network and Sharing center > Advanced sharing settings > File sharing connections. Use 40 or 56-bit encryption option to see if the freezing issue is related with that.
It probably may not be the case. Your issue got my attention when you said it has happened when you started your Windows 7 computer. It might be related with the network packages that Windows 7 sends over the network during startup. Though I haven't done any technical analysis over this. Just a hunch.