I rebooted and all is well. I was able to upload the photo without any problems. I had tried uploading it earlier, but it was too big so I resized it to less than 250kb and then still couldn't upload. I suspect I had something in my cache. At any rate, all is well. Thanks for your help!
When you first attempted to upload the image that got rejected because it was too big, the details of the filename got logged in the Cafe's record. When you attempted to upload a second time the system assumed that you had already posted the picture once and wouldn't let it through a second time.
If you had changed the (jpg) filename, before uploading a second time, it probably would've accepted it without the need for a reboot.
If anyone is wondering whether or not you could post two images with the same filename the answer is yes - the Cafe makes an amendment to the name of the second and subsequent uploads. This happens in the background and you only see the results.