Opera 11.10 gives me the following error when the page with the sockjs-client script is loaded:

I understand that Opera 11.10 is close to 6 years old, but it's still a regression from 1.1.1.

Unfortunately I don't have the skillset myself to investigate and fix this issue, any help is appreciated. Opera 11.10 can be downloaded from http://www.opera.com/download/index.dml/?ver=11.10.