Your browser does not seem to support JavaScript. As a result, your viewing experience will be diminished, and you have been placed in read-only mode.
Please download a browser that supports JavaScript, or enable it if it's disabled (i.e. NoScript).
I have the same issue, it is caused by resourcepacks I believe. You can disable all but vanilla from the options.txt
edit: why i believe it is the resourcepacks is because disabling the developer pack stopped this error
