IE 7 is not using htm on my machine

As I understand htm and html are different animals. An a website we use for
our multiplayer flightsim. we have a kneeboard which connects to our website.
When we fly data is placed on our kneeboard. This has ll pertinent info of
the airports we fly to and from with maps and various calculators for flying.
Some are time/speed and wind variables. One calculator is heading/distance
where we choose one airport then another the hit 'calculate' - we are then
given the heading from the first airport to the second plus the distance
between them.

This calculator no longer works. It runs under htm I am told. Everything
else on the kneeboard works fine. This is the only one under htm and it no
longer works on my machine, whereas last week it was just fine.

Is there a setting I need to use in tools- internet options to reactivate
this? Or am I missing some file somewhere? Bob