If you are using the HealthVault API, you may be running into the following issue:
HealthVault does not properly handle comments or whitespace between XML elements when a request is made to the XML API. Because of this, partners using the HealthVault XML API directly, instead of the SDK, may encounter errors. The HealthVault XML API methods do not return consistent or accurate error messages for this problem. Partners that receive any unexpected errors should ensure there are no comments or whitespace between elements in the XML request.
We are actively working on a fix for this issue and regret any inconvenience.
Remove any comments or whitespace between XML elements in requests to the XML API.