Could you send the FDF (fitting function definition) file, sample data, and initial parameter values to us? Our e-mail address is tech@originlab.com.
To locate the FDF file, open Windows Explorer and find the \Origin\FitFunc folder. Sort Explorer based on the Modify date and you should see your function appear at or near the top of the list. It's name will be something like "user#.fdf" where the # represents a number.
We look forward to hearing from you.
Sincerely, Ryan Toomey Technical Support OriginLab Corporation