Hi,
There was a small problem with your WDM 1×2 component. I believe you were trying to determine the BER of a single frequency channel. If that’s the case then you need to make sure the channels of your demux match up with the channels that are being transmitted. Attached is a quick fix I made to your project file. Just look at the properties of the WDM 1×2 component to see the changes I made.
Regards