"Cannot redeclare class calendar" error message

Problem:

I've installed and enabled the shared calendar plugin but when i go to my setup to test it, I get this error message:

Fatal error: Cannot redeclare class calendar in .../calendar.php on line ...

This is caused by the smallcal plugin, Shared Calendars has it's own version of the small calendar that shows up in the left pane

Solution:

Disable the smallcal plugin in config/config_local.php