Patch 6.2 LolClient Interface Error

Since finishing the 6.2 patch, I've had a recurring error. After logging into the client, an error pops up as soon as the main interface pops up.

"Error. There was an error processing a message from the server; this may be caused by a number of issues so it is recommended you restart your client. If it occurs to continue please visit support.leagueoflegends.com with a description of the error and what you were doing at the time."

After I "OK" the message, there seems to be no further issues. I can play matches regularly, earn IP, etc. It only happens once upon every login.

Support says it's a known issue they are working on. Anyone else having the same problem?