Update: New problem - read under Edit 3 below for details...
I think I finally have fixed the issue... I hope.
There must have been an error while I transferred the files over from old hard drive to this one... I have installed a brand new version of GTA2 (the stripped version from GTAMP) and created a new MIS file with the same details and compiled it in Vikes compiler and it works! Also, it even loads in the official GTA2 compiler as well and not suddenly close.
Now then, I think I can finally carry on with this... time to copy the scripts and maps over to new folder while leaving the essential files intact in the new installation
Edit - as soon as I moved the bulk of the maps/missions/scripts over to new folder it came up with the same error... there must be a troublesome file somewhere in the data directory...

And also, I can't seem to get the powermanager to recognise my new GTA2 folder to enable debug options (I have up to 11.3 beta 6 exe by Vike and even tried using the registry thingy as well). I get all the fun I swear
Edit 2 - Going to try and install the official free version of GTA2 from the Rockstar site and use the contents in the "powerpatch" registry file from GTAMP and apply it to the new version... hopefully it'll work!
Edit 3 - Still no luck. Installed a fresh copy from the official installer and even did the powerpatch thingy and used the updated GTA2 exe (v11.3 beta 06) and tried using manager-hkcu.exe (as it says in the post about it) and I still don't have any debug options? What am I missing/doing wrong? If someone could explain from scratch (from installing either the light version or official version will do) and how to make it work properly I'd be very grateful! Preferably easy steps to follow and in correct order, I think I may just be too old/forgetful! Thanks to anyone who can help... Oh, and the frame-rate seems to be a little sluggish too, any fix for that?