RPC stands for Remote Procedure Call.
It means that a request from your computer to the Photobucket server to perform the desired action was not properly sent or received.
it may be due to to much trafic on your ISP or the remote site been overloaded (most common causes).
You just need to wait a little and try again.
If after a few trys it still don't work, please contact the support a photobucket.
Electro, April 2011
