Recently The PC Support Group were contacted by a customer whose Windows server backup was failing, with error code 2155348129. Typically we don't use Windows Server Backup because the reliability and features are somewhat lacking, however this customer chose to use it for price reasons.
It turns out that the cause of it not working was down to a Sharepoint update (SP1 to be precise). This has been blogged on the SBS Technet site.
Backups failing is a real concern for business. Once configured, do ensure that someone is receiving notifications of its success or failure. You can do this with the Reports feature from the SBS Console.
