Sorry you’re experiencing issues. Have you been able to draw boxes under any circumstances, or just when you’re trying to follow along with the closet video? One thing you can do to see if you can draw any boxes at all is to go to File -> CabWriter -> Re-Load Factory Settings (then re-save your file), which will set everything back to factory defaults. After that, try drawing some cabinets. If that works, then you can start changing parameters again one at a time, or in small groups at a time, and draw more cabinets. If you get the error again, you’ll know which parameter is causing it. You have some combination of parameters currently set that is not allowing a cabinet to be drawn without an error, so you want to get back to a known set of parameters, then work your way back.
Let us know if you continue to have problems. You can also send us your SketchUp (.skp) file for us to take a look at…