Integrating with TinyMCE
Most of WYSIWYG (What You See Is What You Get) editors generate some HTML tags for an empty string. So, basically, you can't use notEmpty validator to validate a text area which uses a WYSIWYG editor.
Instead, use the callback validator to get the raw HTML string, and check if it's the default value generated by the editor, then it's empty field.
The following example demonstrates how to do it with the TinyMCE editor.
TipYou should look at the basic principle when integrating FormValidation with 3rd party libraries
The following validators might be useful to you.