Help with BGT Installation

Hi All,
 
I have just downloaded and installed a BG: The Original Saga and the BG2: Complete from Gog.com. I then downloaded and installed the BG2 Fixpack (freshly downloaded v10 from Gibberlings). The next step was to install BGT so I downloaded it here (v1.18). The installation was progressing them I hit this error:
 
Installing fixpack...
Copying and patching 43 files ...
Copying and patching 19 files ...
ERROR: illegal 2-byte read from offset 1148 of 1148-byte file arghai.cre
ERROR: [arghai.cre] -> [override/arghai.cre] Patching Failed <Copy> <Failure<"arghai.cre: read out of bounds">>
Stopping installation because of error.
 
Any help would be very welcome!