Same here, when I get in install program upon installing files it says:

Current file: CRYPTIC.SSI Runtime error 005 at 0395:008D.

Somehow I managed to get it working now.

So I've tried installing this addon with GAMER but I so far got 4 different runtime errors. I tried tppatch, dosbox, in dos but no matter. Seems the SSI file is some kind of archive that can only be installed by GAMER.

Try Doombuilder