Peter T -

First off I want to thank you mightily, you pointed me in the right
direction, I changed part of the code to the following, and now it works

Set Y_data_range = ActiveSheet.Range(y1Axis)
Set X_data_range = ActiveSheet.Range(x1Axis)
Set Y_est_data_range = ActiveSheet.Range(y_EST)
Set X_est_data_range = ActiveSheet.Range(x_EST)
sY_data_range = "'" & ActiveSheet.Name & "'!" &
Y_data_range.Address(ReferenceStyle:=xlR1C1)
sX_data_range = "'" & ActiveSheet.Name & "'!" &
X_data_range.Address(ReferenceStyle:=xlR1C1)
sY_est_data_range = "'" & ActiveSheet.Name & "'!" &
Y_est_data_range.Address(ReferenceStyle:=xlR1C1)
sX_est_data_range = "'" & ActiveSheet.Name & "'!" &
X_est_data_range.Address(ReferenceStyle:=xlR1C1)

I cannot begin to thank you enough. That was extremely bedeviling error to
get through.