TOPIC: unknown value while evaluating 'totalweight'

Hi Reinhold,
This is following a previous ticket called "Help needed to create rule on shipping wine"
Here is an update:
I purchased the Advanced Shipping Rule for VM Plugin by the way.
I have put all the weights for the products accordingly, 1 for bottles, 2 for magnum, 0 for tickets.
I have changed the formula to this:
TotalWeight<=18; Shipping=20
TotalWeight>=19; Shipping=0
I get an error message and no freight is added over 19 bottles:
Evaluation yields unknown value while evaluating rule part 'totalweight'

This was the previous formula which worked fine but not with concert tickets obviously:
Articles<=18; Shipping=19
Articles>=19; Shipping=0
I need to resolve this asap. What am I missing ?
Can you help please? Thanks a lot

Dear Eric,
As I wrote in the other reply, too, the variable is called "Weight".

Best regards,
Reinhold