I have had this same problem (Win 7 x64) with BAIB 2013, ASIO4ALL, and external USB sound devices (ART and TonelabST-not Lexicon), and discovered that it would resolve if I started another music program which used ASIO4ALL (Reaper in my case). I played with both RealBand and BBW and discovered I could cause the problem by removing a device (internal sound device) from the ASIO control panel from within either program. Then I would get the same error you describe. Restarting the program wouldn't help. My first solution was to start Reaper and configure ASIO. Then the RealBand and BBW problems disappeared.

I discovered that the problem could also be solved by choosing an MME driver, playing something in RealBand or BBW using the MME driver, then EXITING (critical to exit) RealBand or BBW. When you restart BBW, you can choose an ASIO driver and configure it, and it works. Since you're using MME now, you could just restart Band in a Box, configure ASIO, and it should work. Your device may also be usable with ASIO4ALL if this solution dowsn't work with your ASIO driver. My TonelabST has its own ASIO driver but also works fine with ASIO4ALL.

It may later redevelop, which it will on my computer if I start RealBand or BBW without my USB sound device connected. Then ASIO4ALL defaults to the internal sound. If I then try to remove that internal sound device, the problem will always recur.`

You might try this and see if it works for you.