I think its something related to the iTunes/Apple passwords stored in Keychain Access.
Ive had iTunes Match since it first came out way back when (in 2011 I think?). I had this issue up until a few months ago on two of my Macs when all of a sudden the problems disappeared.
Then yesterday I decided to go through the Keychains on one of my macs and because I am OCD i started deleted saved passwords/logins/etc that I thought I didnt use anymore. I deleted so many logins, local items, system items, and system roots....
I have now gotten this error message three times on this mac.
I dont know which type of stored login or system item I deleted that would cause this. But based on cause and effect Im pretty positive this narrows down where to look for a solution.
Rich