keytab regeneration stage failing - upgrading to HDP 3.0.1 from 2.6.5

[#1]

When upgrading to 3.0.1 from 2.6.5 from Ambari I am getting following error message

An internal system exception occurred: Unable to build keytab regeneration stage

Any idea?

Where should I look for exception error?

Tried restarting KDC but of no help.

[#2]

After some investigation foend that

KDC Administrator Credentials to the Ambari Credential Store was not properly set.

Then set it from Ambari and it started to work