v3 files are definitely not backwards-compatible with v2. If you're seeing this in v2, and you've recently installed v3 (to try it out ... or for whatever reason), v3 will install its templates over top of the v2 templates. So now all of your templates are v3 and when you run v2 it can't load any of those templates. To fix this, go to the Preferences tab, press the Data Stores button, and look for the "Active" Data Store. Right-click on it and select "Initialize". On the dialog that opens, check the box next to "Always overwrite existing files", then press OK. After it finishes, exit and restart the TD.