Mailman Error “Bug in Mailman version 2.1.11.cp3?

If you are getting following error when trying to modify mailinglist then execute following command on shell

Error
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Bug in Mailman version 2.1.11.cp3

We’re sorry, we hit a bug!

Please inform the webmaster for this site of this problem. Printing of traceback and other system information has been explicitly inhibited, but the webmaster can find this information in the Mailman error logs.

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Command

chmod 02775 -R /usr/local/cpanel/3rdparty/mailman/