I spend a lot of time over on Zooomr, posting photos, looking at other photos, and chatting on Zipline. There have been some pretty consistent complaints about uploads not working over the last few weeks.
Most of these problems were solved last week, but some people were still experiencing either intermittent problems uploading certain photos, or problems uploading ANY photos. I had two shots that I could not get uploaded, no matter what I did with them. After much frustration, I narrowed the problem down to some metadata that was giving Zooomr problems.
The problem area is the IPTC Caption field. Photos with any data there will not upload properly. However, it is easy to fix this when you are editing your photos. If you use Aperture, look for data in the Caption field. It will look something like this:

Just delete the data in the Caption field.
If you use Photoshop, click the File menu and then select File Info. In the IPTC Content section, look under “Description”. If you see any data there, delete it. It will look something like this:

Once that data is gone, the photo should upload correctly and appear on Zooomr. Note that any data there — even blank spaces — will cause the upload to fail, so make sure there is really nothing there by clicking in the field and hitting delete.
I hope this will help any of you that were having problems uploading certain photos. Happy shooting!