Main report not passing parameter to a linked subreport

Hello,

I have a main report with 1  subreport (I've made this the simplest now in order to troubleshot).

A field in the main report links (or should link) to the subreport, but when I run it,  keep on getting the prompt "Enter parameter values".

The field in the main report is linked to the subreport using the automatic parameter name in the subreport, and have the "select data in the subreport based on field" checked, and the corresponding field in the subreport (shown in the attachment).

I don't know what else to try, this is a bare bones version of the report, so to make sure nothing else is affecting the problem.

I am using Crystal for VS 2013.

This is a winform application.

Thanks for your help

Cecilia