AWS Linux EC2: yum won't run with plugins
Solution 1:
This is most likely caused by a rogue entry in /etc/yum/pluginconf.d/
My first suggestion is to run through each of them in turn, setting 'enabled = 0' on each until the issue goes away, and you'll have found the culprit plugin, if this is the cause.
Alternatively, if this doesn't get you to a fix, increasing 'debug level' in /etc/yum.conf should give you further detail in /var/log/yum.log. The acceptable values are from 0 to 10.