googling makes me think that's a plugin associated with mt.editor from movemen, used for setting mathematical expressions and equations. A trip through .idml might strip out the plugin info.
Download the plugin from internet any url for this please help me!
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Peter's correct, that is either MT Editor from movemen, or its predecessor, InMath.
Do you need to do math typesetting in this document? If not, and if the document isn't specifically telling you you can't open it without the plug-in, you can probably ignore it.
If neither InMath nor Mt Editor are being used for this project and you aren't comfortable just ignoring it, do what Peter suggested - export it as IDML and then open it again in InDesign. That should strip out the call for any unnecessary plug-ins.