How to Output MXF with MPEG2 for broadcast

Our TV network requires a delivery in MXF (or GXF) :

[MXF or GXF wrapper (GXF preferred), Mpeg 2. Video format: SD Long GOP 4:2:0 @ 8 - 15 Mbps]

I have output the MPEG2 file from FCPX. However, Compressor won't allow me to embed the MPGE2 file into the MXF with CC. The job fails, with "Quicktime cannot open this source file".

Any suggestions?

thanks,

Geoff