disabled button and Cannot read property 'length' of undefined

[Paweł Lubczyński]

i got an error via ajax request

Uncaught TypeError: Cannot read property 'length' of undefinedjquery.js:357 jQuery.extend.eachyiichat.js:90 jQuery.ajax.successjquery.js:3119 firejquery.js:3231 self.fireWithjquery.js:9275 donejquery.js:9685 callback'