I've find a temporarily solution.
I have my array like that :

A | B
NameTitle1 | NameTitle2
Value1 | Value 2
Etc.

If I choose the two columns, my graph is not the one i need, but if i put an
empty cell instead of "NameTitle1" in "A1", the graph is better, with the
column A on abscissaes, and the column B on Ordinates.

If you have a better solution tell me ;)