If I had to take a guess the reason is that you are only presented with the variables of the same data type. If you click on the variable you want to edit, then "Edit Caculated Variable" you should be able to edit it.    In the example below, you can see that the process input variable is expecting a data grid.       If you click on the pencil box next to the value you want to set     You will be taken to the area to select the appropriate variable. Because the input type is Data Grid then we are only presented with data grid variables. Select the variable you want to edit, then click the pencil box on the right side.     Now you have the properties box for the calculated variable that you want to set.     Make your changes and then click okay all the way back out until you are back to the diagram.       ... View more