Hi glennpackham,
Thanks for purchasing the Events Calendar.
I took a look and see what you are describing.
It looks like a small compatibility issue with the way your theme is setup and how our plugin is setup that is causing the issue. It is not to say either one is doing something wrong, we just do things a little differently and that causes the issue.
So adding something like this seems to help part of the issue:
.error404.events-archive .entry-content {
max-width: 1040px;
padding: 0 376px 0 60px;
}
Since your sidebar is placed absolutely you will have to add some more css to get it to how you would like.
Let me know if you have any follow up questions.
Thanks