I ran into this and found it rather unfriendly, when I wanted to refresh the mod_cluster manager (mcm) server returned Error 500. This happens when the last command was operating with a node which is no longer in the list. For example disabling a context:
You can easily run into this since there is no clear way - a link - to get to the page without any parameters (supposingly following the Autorefresh link which is not always desired to turn it off).
Thanks for considering!