"An error occured while uploading to Imgur: Value cannot be null. Parameter name: key"
This just started happening in 1.02.2011.
Is the problem still there? It might be an issue with Imgur selber.
Anyway, I made a lot of changes for the RC3 which I hope will prevent this issue.
It should be available soon.
It appears to be working OK today.
as it is working, I'm closing this ticket.
But with 1.0 RC3 I changed the imgur upload a lot, so I won't mind if you tried this and let us know if this works.