Problems syncing tomboy in Oneiric

I read the list of similar bugs, and none of them seemed exactly the same as what I'm experiencing. If this is a duplicate, I apologize.

I'm running tomboy 1.8.0 in Ubuntu Oneiric (11.10) and trying to sync with my other computers via Ubuntu One. At first, I'd get to the part where it told me to click 'save' and the 'save' button was greyed out. I found someone online who had solved this problem by changing https in the address to http. I tried this and it worked, briefly. The synchronization started, but then stopped and I got the 'failed to synchronize' message.
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The tomboy.log contained the following:

12/9/2011 9:45:57 AM [INFO]: Initializing Mono.Addins
12/9/2011 9:46:14 AM [ERROR]: Synchronization failed with the following exception: Unexpected character '<' at [2:0]
  at Hyena.Json.Tokenizer.UnexpectedCharacter (Char ch) [0x00000] in <filename unknown>:0
  at Hyena.Json.Tokenizer.InnerScan () [0x00000] in <filename unknown>:0
  at Hyena.Json.Tokenizer.Scan () [0x00000] in <filename unknown>:0
  at Hyena.Json.Deserializer.CheckScan (TokenType expected, Boolean eofok) [0x00000] in <filename unknown>:0
  at Hyena.Json.Deserializer.Deserialize () [0x00000] in <filename unknown>:0
  at Tomboy.WebSync.Api.UserInfo.ParseJson (System.String jsonString) [0x00000] in <filename unknown>:0
  at Tomboy.WebSync.Api.UserInfo.GetUser (System.String userUri, IWebConnection connection) [0x00000] in <filename unknown>:0
  at Tomboy.WebSync.WebSyncServer.BeginSyncTransaction () [0x00000] in <filename unknown>:0
  at Tomboy.Sync.SyncManager.SynchronizationThread () [0x00000] in <filename unknown>:0
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I ran 'tomboy --debug>~/tomboyDebug.log and got this, repeated four times:

(Tomboy:2476): Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap",