When installing Azure Backup on to SBS 2011, the installation fails with Error 2145124329, and does not complete. It appears Windows Management Framework 3.0 is required for the Azure Backup agent to install correctly, however Exchange 2010 does not support WMF 3.0.
This article goes into better depth on what issues WMF 3.0 causes on SBS/Exchange;
Luckily I have just completed migrating all the e-mail from Exchange 2010 to Exchange Online, therefore I uninstalled Exchange. Once this was uninstalled, I then manually installed the WMF 3.0 and the Azure Backup Agent install completed successfully.
Interestingly enough WMF 3.0 did break the SBS Console (but who cares because it's horrible anyway)! Moral of the story is, if you are using SBS 2011 and can't rip Exchange off the box you can't use Azure Backup.