Known bug in Version 6.0.00 that appears when creating an rgu file sometimes. Fixed for next release.

Here are the steps to fix it in Version 6.0.00:

Go to the Equipment tab. On the equipment tab, select the app/light tab (make sure this is the old appliances screen that is part of the equipment tab). Delete the dryer. Save the file. Run your calculations.

It is safe to delete this app/lights tab dryer on every file you register -those inputs are only used for non rating purposes. 

We should be releasing our next versions in April with the fix. Thanks for your patience.