AVI export usually succeeds in the 'free' (trial) VP version. Save Project File AS routinely, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite. Then you can restore a project to the state it was in when saved. Just double-click the VPJ file (which isn't playable).
Then uninstall Videopad via Control Panel | ADD/REMOVE PROGRAMS.
Install this version and see if the export capability returns.