language assignment issue in Compressor

I bought Compressor today.

I'm on Mac O/S 10.13.6 using FCP X.

I created a file with closed captions - format CEA-608 and language is English.

Took the master file into Compressor.

When I try to output, it returns the following error:

I changed this in Inspector:

But I'm still getting the same issue.

What do I need to do to fix this?

In FCPX, I have the format set and the roles:

I need help pretty urgently, and Apple keep suggesting I ring the US for help, which is simply not an option for a starving artist from the UK.

Thanks

Heather