Can't find `xetex.fmt'

Hi,

I just installed XeTeX v0.98 using i-Installer, never having used it
before, and I get this message when trying to typeset (in TeXShop):

This is XeTeXk, Version 3.141592-2.2-0.98 (Web2C 7.5.3)
 %&-line parsing enabled.
kpathsea: Running mktexfmt xetex.fmt
fmtutil: format `xetex' not available.
I can't find the format file `xetex.fmt'!

I realise this has perhaps been addressed before in different forms on
the list but I couldn't ascertain what the accepted solution was. Help
would be appreciated.

Thanks
Laurie Field