Equations: Getting an Error

Hi,

I have created an global variables. And while working with a part I have deleted a feature which no longer in use.

Then I notice the Equations folder or tree turns to color RED.

How do I correct this error. As I do not know that is Equation 54: "D1@Sketch23"?

Appreciate any help.

Thank you,

Willie

SolidworksDrawings And Detailing