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Description
One of the elements of the inverse of Rk, which is defined in the Measurement Window , has an absolute value greater than the value limit in the Debug Fit dialog.

Suggestion
Either increase the value limit or change the value assigned to Rk in the Measurement window.

Diagonal Case
If b is a vector and B is the corresponding diagonal matrix , the inverse of B is the diagonal matrix corresponding to the element by element inverse of b.