I'll retry it periodically or open another channel, might be a connection or routing issue.
Update: Eclair failed to send through lightning too, it worked for me, tried just now (maybe your client was closed for some reason?).
I just checked it now, my channel disconnected for some reason. Tried to restart Electrum, but still couldn't get it reconnected. Well, that one's a gonner. I'll open another channel and post another request tomorrow.