Why do I have to force quit Aperture every morning because it can't connect to Flickr?

I have Aperture 3.3.1 and iPhoto '11. I have just started viewing and using my iPhoto library in Aperture rather than importing it all into Aperture, and am loving it. However, every morning after the iMac has been to sleep overnight and I wake it up, the Aperture icon in the dock starts jumping and I get an error message: "There was a problem connecting to Flickr OSStatus error -1." There is a whirling line at the bottom of the Aperture window saying it's trying to connect to Flickr and when I press the OK button on the error message it beeps but nothing happens. This means that I cannot use Aperture, nor will it let me quit it because I can't get rid of the error message. I have to force quit the application but then when I re-open it everything is fine for the rest of the day, even when the computer goes to sleep – until the next time I wake up the iMac after an overnight sleep and the error message comes up again.

I am so scared of losing any photos in Flickr that I haven't dared try to delete my com.apple.Aperture.plist in the Preferences Library, or the com.apple.Aperture.plist.lockfile. Please can someone tell me what to do that won't compromise my photos in Flickr? Many thanks.