On researching this error further, it seems the correct resolution is to upgrade to the current version of the plugin, which you can do either by downloading it and re-uploading to the server, or by deleting the version that's currently installed and reinstalling from the admin panel.
If you don't have direct access to the server, either through ftp, a web-based file manager, ssh or some other method, you should get a hold of your server administrator to help resolve the issue.
Please note that the broken version is 0.6.1, which has been removed from the tree. The cause of the error in that version was poor housekeeping on my part, which led to some leftover merge data in the code. It's been removed and fully repaired in 0.6.2.