INCLUDE filename must be a string constant

Following the keyword %Include, you specified something other than a quoted literal. For example:

Dim myFile As String
myFile$ = "C:\myroot\myfile.lss"
%Include myFile$                    ' Illegal because %Include takes a
                                    ' quoted literal 
%Include "C:\myroot\myfile.lss"     ' Correct syntax

Use a quoted literal.