Webalizer showing strange behaviour

I am trying to get webalizer to show also last year's data, the default report selection interface doesn't have the option to select a year, but I did find in the man pages of Webalizer that I can set the options GraphMonths and IndexMonths. I added both options to the global Webalizer config file /etc/webalizer/webalizer.conf with a value of 60.

However when trying to generate the report I get the following errors:

Warning: Invalid keyword 'GraphMonths' (/etc/webalizer/webalizer.conf) Warning: Invalid keyword 'IndexMonths' (/etc/webalizer/webalizer.conf)

What is wrong here? How can I make webalizer show more than just the last three months?

Thanks for helping!