On starting my Kubuntu 10.04 the other day I got something like this
How do I make the clock a normal size so that there is room for my windows?
Looks like a corrupted config file. Try to create a new panel and drag the widgets from one panel to another. If that doesn't help, create a new panel and add new widgets. If that doesn't help, then you might need to delete plasma config files (make a backup).