You can not delete the default template, I guess:
you must have renamed it?
Start a new file, import the model (as model, you might want to ‘unwrap’ the outer shell first) a make a new report ([File]->Generate Report and start from there…
You can save the report to model or export it as GRT (Generate Report Template) file
here are the files:
Truss.skp (2.2 MB)
had to zip the .grt file…
Truss Report.zip (532 Bytes)