"The primary cause of this discrepancy was that one piece of ground software supplied by Lockheed Martin produced results in a United States customary unit ('American'), contrary to its Software Interface Specification (SIS), while a second system, supplied by NASA, that used those results expected them to be in metric units, in accord with the SIS."

That's in reference to the Beagle 2?

Yeah, that's in reference to the failure of Beagle 2. It's on the page that was linked by Someone1234 (https://en.wikipedia.org/wiki/Mars_Climate_Orbiter#Cause_of_...).

The Beagle 2 and Mars Climate Orbiter are not the same thing. It is unknown why Beagle 2 failed and there is no reason to believe it was due to any unit mismatch. It may be that two of the solar panels failed to deploy.

It's well known that the metric solar panels failed to deploy. The imperial solar panels opened successfully, but that did not generate enough electricity to keep going.