Arthur I think everything is working as it should. Here are a few comments on your spreadsheet that I hope will help:
You need to configure XLC on the XLC Pro mode to loose the "non-commercial message" by
following these instructions.
The error message "#CellD26 not named" simply tells you that cannot build an algebraic equation because D26 is not named. I can see that cell D15 is named its name is Whs and this will be inserted into an equation. The
tutorials cover this.
You don't necessarily have to name all your cells. You may choose to display numeric equations rather than algebraic equations in which case naming is not required.
Tutorial 11 covers this.
XLC default options are set by following
tutorial 6.
I have updated your spread sheet following
tutorial 3. Please find attached.