Using the script THENICEONE made - I did the install with OBMM
But when I try to activate Mart's Monster Mod 3.7 I get told that FCOM is not installed
What is the issue?
No issue really. It warns that you don't have FCOM, which you shouldn't when installing MMM, so it's OK.
Also, I'd recommend using the existing release threads rather than starting new ones. In this case: http://www.gamesas.com/index.php?/topic/995334-mmm-and-fcom-omod-installers/.