[XeTeX] Font mapping

[Alastair M. Paterson]

Hi!
I'm just starting to use XeTeX (MikTex 2.7 on Windows) and am trying to 
get a non-Roman script file to compile.

A unicode font has been installed (used fc-cache) and the text is 
produced correctly however there needs to be a mapping to convert 
'ASCII' numbers in the text to the specific characters of the language.

In the file is the following line:

\def\regular{"Uchen_05:mapping=Latin2TibetanNums"}

In the same directory as the project files, are the following two files:
Latin2TibetanNums.map and Latin2TibetanNums.tec

However, the log file produced when the XeTeX command is issued produces 
the following:
Font mapping `Latin2TibetanNums.tec' for font `Uchen_05' not found.

Any suggestions as to what is happening or how to solve this would be 
greatly appreciated.

Thanks

Alastair