Enable the watermark, can't use browse server

Hi, everybody, I use CKEditor 3.X and CKFinder 2.X, If I disable the watermark plugin ,I can upload the Images and use the BROWSE SERVER , but if i set the config.js by 'config.extraPlugins = 'watermark';', enable the watermark plugin and click the BROWSE SERVER button, and open a blank page, the ckfinder.html can't load the Images for borwser.

I use for php projects. Thanks~