Hello everyone,
I created a validation rule on a metadata control : 
,
however the rule never works. I can validate the forms even if the metadata control is empty.
And when I try to connect the metadata control to one of my list metadata column I get this alert :
Error message in the logs :
"Failed to retrieve form control for canvas. Error: Object reference not set to an instance of an object.."
My version of Nintex forms is 2.9.1.0 and Nintex Workflow is 3.1.7.0
Any ideas ? Thanks for your support