The full error message is, I believe, 'Experiencing a network error', which fits the problem.
Can you still browse the web while that message is being displayed? Did you type this very error report while the message was being displayed in Photosynth?
In my experience the report from Photosynth invariably goes hand in hand with loss of all internet connectivity due to local network woes. Usually, if I just right-click on my network activity icon in the system tray and choose 'Troubleshoot Problems', my machine's IP address is refreshed with my router and everything comes back - web, IM, Photosynth, etc.
If you get the message displayed while the rest of your internet activity goes unhindered, though, I don't know what to tell you.
Does this same error occur when you try to upload an actual synth, rather than a panorama?