Problems with TMinuit Contours

Hello ROOTers,
I’m doing some minimizations using TMinuit. I then want to plot the confidence countours of the parameters. I use the method TMinuit::Contour() . However, for some parameters it fails with the error “MNCONT UNABLE TO FIND FOUR POINTS” . I understand the error message, but it’s not clear why this is happening. My fit is pretty complex and the problem might depend on the fitting function. What shall I do/try?

Thanks in advance,

Could you post teh shortest possible RUNNING script (and data set) explaining your problem?