Thanks Peter,
Yes if you unset the orientation eg by clicking the icon at the bottom of the image frame it does as you say then display the image but with the original orientation. It is most peculiar as as moving the mouse over the greyed out image to locate the high counts where the stars are does confirm it actually performs the reorientation and you can display the brightness histogram etc but it just refuses to display the image for some reason. I guess there must be something odd about the image that it does not like. It is a pity as my intention was to give it a plate solved spectrograph guider image and overlay it on a DSS/SDSS image to check the position of the slit is correct for objects which are too faint to see in the guider exposures. I will reread the manual and perhaps try some other images.
Cheers
Robin