[Help-glpk] Operand preceding = has invalid type, while trying to implement VRPTW

[Navjot Kukreja]

Hello everyone
I am trying to model a VRPTW, rather a Dial a ride problem using MathProg, to 
be solved with glpsol.
I started from the base code by Jeffrey Kantor shared on this mailing list, but 
faced the error: "Operand preceding = has invalid type" while trying to 
implement a constraint for maximum number of stops that should be there between 
a customer's start and end node.  Could someone be kind enough to look at the 
code and help me understand the reason for this error and how I can correctly 
implement this constraint?

I have attached the file here.

Thanks
Navjot Kukreja

aircraft.mod
Description: Binary data