R help - Feb 2007 - sprintf error clustering with rattle

Hi,
I'm an italian R (and data mining) beginner.
I installed R, Rattle and rggobi with no trouble.

But I'm not able to do clustering (both kmean and hierarchical).

When I press F5 in Rattle Cluster tab nothing happens (and no log rows in
the Log Tab).

On the R console I get the following error (in italian):

"Errore in sprintf(fmt, ...) : argomento di lunghezza zero" (it means
zero
length argument)

I set only input variables (no target).

Could anyone help me?

Bye

Amerigo