Not allowed to install Matchcad 8

I have had Mathcad in versions 5, 8 and most recently 9 installed on my pc.

I then removed versions 5 and 8 to gain storage on my pc

Now I need to reinstall version 8 to be able to work on the same sheets as my teammates. However, when I go to install, it says that version 8 is not allowed.

Any suggestions on what to do?