Actually,I did what cipper told me for 2nd time and now told me the following: ...Selecting previously deselected package gnuplot.Unpacking gnuplot (from .../gnuplot_4.2.6-7_all.deb) ...
Errors were encountered while processing:
/var/cache/apt/archives/gnuplot-x11_4.2.6-7_armel.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

The app manager is not open while this command is executing
I hope you understand that the 3 stops in the beggining mean that there is text but I didn't write it because it says:Connecting to repository.maemo.org,downloading bla bla bla

What is going wrong???