gMinuit variable "lost"

ROOT gives

Error: Symbol gMinuit is not defined in current scope al.C:79:
Error: Failed to evaluate gMinuit->GetParameter(1,alpha[0],alphae[0])
!!!Dictionary position not recovered because G__unloadfile() is used in a macro!!!
*** Interpreter error recovered ***

when I try to run a script a second time in the same ROOT session.

The script contains

#include Riostream.h

/* … */

h1->Fit(de);

gMinuit->GetParameter(1,alpha[0],alphae[0]);
gMinuit->GetParameter(3,alpha[1],alphae[1]);

I checked the dimension of the arrays alpha* just to make sure, but the problem persists. What is the problem?

Before executing your macro, do

gSystem->Load("libMinuit");
Rene