Problem with .mds and .mdf files.

I have recently got a software which is in the .mds & .mdf format. I used Alcohol 120% and burned the file on a CD (from burn image wizard I selected .mds file) .

I then installed the software on my PC from this CD. Now every time I start the SF it asks for the CD and when I enter the CD the following message appears : "original disc could not be found or authenticated"

Can any one please help?

Thanks