Not sure what was the cause in your case, but since we see this happening more frequently in the last few days it might be in connenction with things like the Raspberry Pi Beta tests and the connected "donation" of extra resources and/or the release of system version 0.6.0 and/or maintenance and/or server issue and any combination thereof
Also these reasons
There also was some problem with load balancing yesterday, which should have been cured already.