Virtual Box - Critical Error after Host ReBoot

[silliemunkie]

hello all,
I installed VirtualBox on my WinXP machine, and created an Ubuntu guest with no problems. After I rebooted my WinXP machine, I get the following error when i try to launch Virtual Box:

Assertion failed at 'C:
\vbox\branch\w32-2.0\src\VBox\Main\VirtualBoxImpl.cpp
(306) in VirtualBox::init

Unknown exception

I have uninstalled and reinstalled, but get the same error.

thanks,
Jason