Chuck,
Importing registrations from outside the practiscore site is very touchy. One extraneous space or period will screw the whole thing up. please take a look at this tutorial it seems to work for everybody 100%.
At this point if you have not shared the match around and it’s only imported shooters you might dump the whole thing and create a new one using the importing tutorial below. The other option is very time-consuming to try to find what’s wrong with the spreadsheet you imported.