Sum formula facing SIZE issue

In “GWP PCL” matrix of the enclosed model, I have a formula to sum “GWP” data from another matrix (GWP Data Matrix).
The formula is GWP = sum(summary(GWP Calculations::GWP)) using LOB Aggregates::Reporting LOB as Reporting LOB Types, GWP Data Matrix::Year as Year
But the formula does not work, I get a SIZE issue and I am not able to understand why. I would be grateful for help on this.
Thanks a lot