Dear Jacques,
In the FCPXML there will be an asset section where it lists all the media that is to be used in the project and a project section that lists how it should be used.
It looks like there is a reference to media r245 lets say it says it has video and two channels of audio but in the project section it is saying it uses 4 channels of audio.
We would need to look at the FCPXML if you could attach it, it might be possible to manually remove the reference for the media, we can give it a go if you would like.
Yours Sincerely
James.