Do not start with a copy of COAS from anywhere else like Steam, or GoG, or from cd, some of the scripts/resource files are incompatible; everything for GOF is already in the Itch link for that version.
Download GOF from the Itch link, then point a shortcut to Maelstrom.exe as Target and the GOF 2.5 folder for Start In, or copy the following files directly into the GOF folder and run it direct from the GOF 2.5 folder:
Buccaneer's Reef
Config.exe
fmod.dll
Maelstrom.exe
Maelstrom.exe._lc