You need to install it for IE. Just go to Adobe's website through IE (preferably IE7) and then download the latest flash player for it and install it. Then run SEUS again.
This same thing happened to me too and I was puzzled as I had Flash player installed for Firefox. But later I realised that we need to install the Flash player for IE for SEUS to work. I think when we install Flash players for browsers other than IE, the Flash player is limited to that browser only. But when we install the Flash player for IE, it gets enabled throughout Windows and other apps which require Flash player can also use it.