In Visual FoxPro 6 SP3, I've just created a form using another developers Class library. There is a right click method in the textbox class with the following code snippet:

IF VARTYPE(This.Value) = "D" .AND. EMPTY(This.Value)
This.Value = DATE()
ENDIF

When I went to run a test on the form, I right clicked on the text box and received an error:

File "Vartype.prg" does not exist.

This.Value was empty (it's value was { / / }). Any ideas why VFP would look for an external prg file for an internal command?