Further to flymail’s post, if using a new version of gimp note that when it comes time to save as a jpg, you need to select " file > export " and NOT " file > save " .
I do not know if this is the case for you, as I note you have the older openSUSE-11.4
If all you want to do is resize or crop an image then it is probably much easier to do it in Gwenview (assuming you are using KDE)
Edit > Resize or
Edit > Crop