Azure table storage returns 400 Bad Request

400 Error means there's something wrong with the value of one of your properties. One way to find out is to trace the request/response through Fiddler and see the actual data being sent to Windows Azure Storage.

Taking a wild guess, I'm assuming by taking a quick glance at your code that in your model you have some Date/Time type properties (OfflineTimestamp, OnlineTimestamp) and observed that in certain scenarios one of them is initialized with the default value which is "DateTime.MinValue". Please note that the minimum value allowed for a Date/Time type attribute is Jan 1, 1601 (UTC) in Windows Azure[http://msdn.microsoft.com/en-us/library/windowsazure/dd179338.aspx]. Please see if that's not the case. If that's the case, then you could make them nullable type fields so that they don't get populated with the default values.

Have a look at Juha Palomäki's answer below as well... there sometimes is a slightly more useful message in the exception where he suggests (RequestInformation.ExtendedErrorInformation.ErrorMessage)

The StorageException contains also a little bit more detailed information about error.

Check in debugger: StorageException.RequestInformation.ExtendedInformation