Space Crusade winUAE

Hello, I was hoping that you fine folks could help me out with some emulation trouble I have.

I have great childhood memories of playing Gremlin's "Space Crusade" on my old Amiga 500, so, I though I would try emulation on my PC I am using the latest version of win UAE and have had great success playing such classics as Heroquest and Cannonfodder:my_rambo: . Hoever I cant get Space Crusade to work.

When I load the game it starts OK, and I get the option screen I select my squads for battle and my mission but when I click on the little grid square on the bottom right instead of the mission loading I get the message.

"Insert data disk into drive" or words to that effect:msn_cry:
Is this a common problem, or am I missing out a step? Help would be greatly appreciated.

A lot of the termonolgy for emulation is lost on me but I have to say it's great fun playing those old classics again.:D