It's likely that your XBMC configuration XML is not properly formatted, or incorrect.
There should be a section in it which lists all of the file suffixes supported by XBMC.
If your file has any of these it will be listed.
-UNLESS-!!!!
You've omitted a opening or closing character to an XML section.
This renders the whole file invalid and XBMC will go brain dead.
The easy way to spot something like this is to use MS Frontpage or similiar XML editor to locate such errors.
