If that error appears every time Windows is started there will be a related entry in your list of Startup items, so you need to delete that entry from the list.
Use Ccleaner to do that, it's easier than using msconfig.exe
Get Ccleaner from here and install it: http://www.filehippo.com/download_ccleaner/
Open Ccleaner, click "Tools", then click "Startup".
Look for the line which contains "Free File Openerunins000.dat", highlight that line, then click the "Disable" button (do not click "Delete" in case you need to restore it)
You can delete it later if you like, but only after you are sure that Windows is working properly.