Yeah, 'fraid it's probably related to having two AV's installed, even if one of them is turned off.
If you can get past the BSOD and look in the taskmanager, you'll probably see processes from both apps running, even with one turned off.
An AV has to get it's drivers/services/magic bits installed at a core level to do its job, and they run at start, turned off or not.
Some antispywares do the same. AVG AS, AdAware2007, and A2, for example, all run services at start, whether the application is running or not.