"The error was due to T: not mapping properly into ram: because of my setup."
There's nothing "not properly" about your mapping

Let me clarify this a bit:

The T: issue was just a wild guess by me because I remembered that once somebody reported sth. similar on AOS4 ages ago (might even have been with a different game). There, IIRC, this was caused by a constallation of T: being mapped to another partition with a "non-standard" file-system which apparently didn't play nicely with the file-attributes being modified which then caused following IDOS->System calls on files I placed there to fail in such a hard way that things got totally blocked.

So it was just a shot in the dark, and luckily for Cool_AmigaN it was a hit
However I didn't further investigate yet what exactly is the cause on MOS. Note that I was able to workaround the issue on AOS4 by doing some changes to the IDOS->System parameters, so it would not happen on AOS4 anymore (at least not on the system of the guy who reported it).

Luckily this issue is really rare in real world, those two reports are the only ones I ever got regarding this on any Amiga OS variant.