Model Builder - "Tool has no parameters"

I just imported a script that I want to use in my model however when I import the script into modelbuilder I keep getting the message "This tool has no parameters."

I know this maybe a fairly obvious question but what does this mean? And why is this preventing me using the script?

FYI: The script is to calculate acreage for a field I created. I know some of the parameters I want to set the 'Type' = Double, 'Precision'=9 & 'Scale' =2.

I am sure I am probably missing the obvious but any help would be greatly appreciated.

Thanks