Alert message when fitting

When I fit around 30 different TH1D histograms (that I get from a list stored in a file) with an user-defined function (defined in my class) I get sometimes a disturbing “alert” message and no fit is done.
What’s the meaning of the alert message?
Is it possible just to disable it?
I searched in the forum and in the documentation but I found nothing.

Thanks in advance!
Below you have the details of my root and system:

ROOT 5.23/02 (tags/v5-23-02@27626, Jul 14 2009, 
Ubuntu Release 9.04 (jaunty)


which message did you get exactly ? It is maybe possible that some of your histograms are empty and then the fit is not done

Best Regards