If an input contains a meta attribute that's not explicitly defined in jquery.validate.js, e.g.

<input type="text" name="myinput" class="{string:true}" />

it fails with an unhelpful "$.validator.methods[method] is undefined" error.

This can be fixed by adding this code on line 471 of jquery.validate.js:

if(!$.validator.methods[method]){ continue; }