If you are getting the following error on the job and it is changing to a pending status:

 
 
On the Exchange server, check the application error log and you may see hpEVA VSS Hardware Provider errors at the exact same time you try to run the backup:
 
[CHPEvaVssProvider::OnLoad]: {--} Returns[0x80004005][-2147467259]
 
 As well as the following VSS error:
 
Volume Shadow Copy Service error: Error calling a routine on a Shadow Copy Provider {21e5ab69-9685-4664-a5b2-4ca42bddb153}. Routine details IVssProviderNotifications::OnLoad [hr = 0x80004005, Unspecified error
]. 
 
On each exchange server, set the following registry key and restart the commvault services.

HKEY_LOCAL_MACHINE\SOFTWARE\CommVault Systems\Galaxy\Instance001\MSExchangeDBAgent\nUseVSSSoftwareProvider and set it to 1.  So it forces the commvault agent to choose the Microsoft Software Shadow Copy provider.