The information you give is a bit short to understand the problem.
Have you set correctly th initial values of the parameters ?
Can you provide a small macro reproducing the problem ?
Which ROOT version are you using ?
On which machine ?
yes by using: SetParameter()
if by any bad chance the value parse to SetParameter() have a problem like (inf, nan)
could it be the problem? I guess there may be troubles, but would minuit return a value out of range?
The code I’m using in relatively complex, so it would take to much time.