Mac Installer on Seagate External Drive causes the application to quit

I have a 2006 iMac running OS 10.5.8 & am tyring to back up using a new Seagate Back Up Plus Drive. When I select & click on the Mac Installer (Dashboard) I get an error message saying tha tthe application dashboard quit unexpectedly. Can anyone tell me what I can do about this & how I can get this to work (via Time Machine)? Any suggestions would be welcome.

Thankls

Wendy