I've never had a problem with DV AVI files before in TMPGenc, but apparently the following may help:
Go: Option > Environmental settings >VFAPI plug-in - right click on the DirectShow Multimedia File Reader. Increase the priority to 2 or move to the top of the plugin list. Now try reloading your video.
If that doesn't work, try using this:
http://www.dvideohome.com/canopus_dv.htm - (apperently TMPGenc doesn't support MS DV AVI 1)