In Exchange 2007 SP3 Microsoft implemented canaries in OWA to help prevent man in the middle/cross scripting attacks in OWA http://msdn.microsoft.com/en-us/magazine/dd458793.aspx#id0080023 gives a good explanation around why you would want to use a canary and what it is. But put basically a canary is a secret between the client and server in OWA this gets stored in cookie collection of your browser and then it gets submitted with the various requests that your browser sends. If your request doesn't have the canary then the server pretty much says "no OWA for you!". Because in the scripting world it can be useful as a workaround to instrument OWA to automate particular things such as enabling the extended junk-Email rule in OWA and Outlook in the past I've posted scripts that use OWA automation that have now pretty much been broken by the canary's. So to fix this you need to add some code that will deal with the canary my favorite object to use for these type of
Pushing the Envelope in Messaging and Office 365 Development