Hi Chris,
Thanks for your quick response and the information is useful. However the error message seems to be a very general error of JavaScript. Could you please follow the below steps to collect more information for troubleshooting?
1, According to the URL, the page appears to be a permission settings page of a library. Please go to the following link and try Show uniqely secured content Option.
http://oursitename.sharepoint.com/TeamSite/_layouts/user.aspx
2, Since the value of ShowUniquePerms is invalid, please collect the source code of the whole page and send to me via Private Message.
1) Go to the page and reproduce the incident.
2) Click F12 in Internet Explorer.
3) Click refresh on the developer tool and then click save to save the source code.
Please let me know if you have any concern.
Regards,
Allan