Hey Tim,
Well, as it turns out, I'm almost positive that I did in fact have 4.5.1 installed. But now 4.5.2 is in and I'm getting the same thing.
HTTP/1.1 500 Internal Server Error
Content-Length: 339
Content-Type: application/json
Server: Microsoft-HTTPAPI/2.0
Date: Wed, 18 Jun 2014 20:13:01 GMT
"The data contract type 'System.Runtime.Serialization.KeyValue`2[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.Object, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]' cannot be deserialized because the required data members 'Key, Value' were not found."
I'm stumped because I'm still not seeing anything in the log file about this. The last entry in the log was from something that happened at 20:10 (GMT).