‘Object Reference Not Set to an Instance of an Object’ When Failing Over an Availability Group Using SSMS <= 17.5


Here’s a quickie that I’ve just stumbled across.

I’ve just tried to initiate a manual failover of an availability group and received the following error.


After a spot of head scratching and thinking that there was something wrong with my AG setup, it turns out that there’s a bug in SSMS.  I was running SSMS 17.5 although this may well also affect earlier versions.

Looking at the release notes for SSMS 17.6, one of the bug fixes that this version addresses is…

  • Fixed an issue when the primary is down and manually failover to secondary, a NullReferenceException will be thrown.

After installing SSMS 17.6 I was able to perform the failover and get things back up and running.

Luckily for me, I came across this while performing some DR testing exercises.  I’d hate to have hit this issue during a genuine DR situation.  Hopefully this post might help someone who does find themselves in that position or at least nudge you in the direction of upgrading your SSMS to the latest version.


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