Inverse gaussian fit

Dear Rooters,
I am new to root and having a big trouble making a inverse gaus fit to my histo.
Histogram (ch1:t) look like this:

Root File:
https://drive.google.com/file/d/0ByFxEx-ojNX6bUFEeGFRRXdOY1k/edit?usp=sharing

I would greatly appreciate any kind of help.

May be you could try this:
root.cern.ch/root/htmldoc/TTree. … nbinnedFit

Thank you, I made it work after recompiling root