Too many audio channels

Hi,
I'm getting this error message.
ERROR MESSAGE FROM X2PRO:
Getting audio characteristics for asset [1-3 (A Only)]
Error trying to create reference for asset (not a WAV file or too many audio channels)

No AAF file has been generated.
X2Pro Audio Convert 3.0.13

To create my synchronised clips I merged camera and .wav files then produced '1-3 (A only)' as an example. All my files are wav so that isn't the problem.

How do I fix the issue 'too many audio channels In FCX? So I can create a new XML file.

Thanks.