Trouble datalogging with DIY ALDL cable

I am using my semi-DIY-ALDL cable. It consists of this: http://www.sparkfun.com/products/8165

I have it hooked up and can read data from it just fine with the key on (obviously) and engine NOT RUNNING.

When I start the engine, I can datalog for up to several minutes or as short as a few seconds and then TunerPro says I have a data error. It will not let me reconnect and when I go into tools to reset the com port, the com port I was using shows up like this {com9} and can not be selected.

I have to restart the computer in order for it to work again.

I never had this problem with the AutoProm. Ideas?