Well, at the moment i myself am still busy discovering the possibilities of MCX, but it's clear that modeldef.xml has two animations with's are named indicator_fuel_quantity. It could be the one in your SDK, but more likely the problem is in the merged model of your C172N.
You can look at the modeldef.xml of the cessna by clicking on the tenth button on the second row of MCX, the on with the white tophalf and yellow bottomhalf (it all so displays the tooltip modeldef.xml editor when your mouse pointer is over it).
Every animation in a modeldef has two sections. The first one tells MCX that there is a animation named indicator_fuel_quantity, it;s GUID, length and a few other things and looks like this.
<Animation name="indicator_fuel_quantity" guid="6585fbde-d8bb-479b-81f1-3f852946c1b2" length="100" type="Sim" typeParam2="indicator_fuel_quantity" typeParam="AutoPlay" />
second section tells MCX what it does and looks like this.
<PartInfo>
<Name>indicator_fuel_quantity</Name>
<AnimLength>100</AnimLength>
<Animation>
<Parameter>
<Sim>
<Variable>FUEL TANK CENTER LEVEL</Variable>
<Units>position</Units>
<Scale>100</Scale>
</Sim>
</Parameter>
</Animation>
<MouseRect>
<Cursor>Hand</Cursor>
<HelpID>HELPID_GAUGE_FUEL_PERCENT</HelpID>
<TooltipID>TOOLTIPTEXT_CENTER_FUEL_PERCENT</TooltipID>
</MouseRect>
</PartInfo>
With modeldef.xml editor you can search and rename or delete a duplicate animation entry. Hopefully that will solve your problem. No guarantees, like i sad i'm still experimenting myself.
