I am using the calculate value expression str(arcpy.Extent(%XMin%,%YMin%,%XMax%,%YMax%)), where the arguments are model variables of type double. Calculate Value runs correctly and outputs space separated double precision values as a string. However, when I run the next process (Extract by Rectangle) I get the warning "All of the processes are not ready to run or have already run" and the process becomes greyed out. (Note: the parameter link in the screenshot is called "rectangle" despite referring to the "extent" parameter)
How can I run Extract by Rectangle with programmatic input for the Extent parameter?

I have had a similar problem with the Extract by Circle tool