This is your currently running correctly version right? The other guy posted issues that included the update from .19 to a .20 version of asterisk. His resolution was to restore as you did. Look for his post on the forum for additional details. He had some ideas of what it was.
If you want to test what is causing the issue yourself, try doing updates one at a time.
Search out the yum commands, you can check for updates to create a current list of what is available. Then try something like asterisk, then elastix and so on tesing between each update. This will give you an idea of which update is giving you the error, read the changes with that version so you can determine what has changed. You will not always be able to just update all software to current versions since they are all being developed separately with their own agenda.
Or since there is some known issues reported just install the update you needed or wanted for a security or functional change to test it and watch for a resolution to be posted to future updates.