Missing Go button for searches

Hi

In my WebHelp project, the Go buttons in the Search pane and for the field on the toolbar are not displayed on the output. I'm using the default skin with some minor tweaks (different book image, different font). The image file, wht_go.gif, is present in the WebHelp output folder, which suggests to me that there's a setting in a file that has gone awry - does anyone know where this might be? Running a repair on RoboHelp hasn't fixed this.

Thanks

Paul