I'm using Ubuntu Edgy (6.10). This is how I fix my problem. Thanks you kelpy2k6.

First, edit the gnumeric OR gnumeric-gtk. (depends on which version of gnumeric is installed, the one I'm using is plain gnumeric):
Code:
sudo gedit /usr/lib/mime/packages/gnumeric
Go to the two lines that looks like this:
application/x-sc;
gnumeric '%s'; edit=gnumeric '%s'; description="SC/XSpread spreadsheet";
Then edit it into one line like this:
application/x-sc; gnumeric '%s'; edit=gnumeric '%s'; description="SC/XSpread spreadsheet";
Then run:
Code:
sudo update-mime