[Gretl-users] Problem with graphs

I've just downloaded and installed gretl, but the graphs don't work. I've uninstalled and reinstalled but it still doesn't work. When I try to get a graph, it opens a gnuplot window and gives an error message: "Invalid byte sequence in conversion input". In fact the message is "sequência de bytes inválida na entrada de conversão" since I am runnig a Portuguese-Brazilian version. Well, I also noticed that gretl uses a directory in "Documents and Settings/Application Data" for temp files. When I ask for any graph, it generates the .PNG temp file and gives the error above. When I click the "ok" button, the png and other temp files are deleted. Any ideas? Thanks Arthur