Good morning to all,

I have Imac with 10.9 and aperture 3.5
also Nik, Photoshop, DXO  and LR4.

Last night, I took a picture with NIK HDR efex Pro 2, did a few things with it  and back to aperture.

then…. from the browser  to Viewer….. no picture , just a grey screen.

I opened a new catalog…..same thing.

I am randomly getting a grey screen in Viewer mode.
When I switch to Bowser mode I can see all the thumbnail images once again but back to grey screen when I return to Viewer mode.
The Loupe shows the image inside of itself but grey around in Viewer mode.
Quitting and restarting Aperture let's me once again sees the images in Viewer mode till it happens the next time and then I have to restart again.
Any suggestions?
Best regards and thank you.

Ray