[Plugin: Visual Form Builder] Warning: unlink

Hi got this after trying to save my form

Warning: unlink(/home/as/public_html/as/wp-content/themes/as/cache/) [function.unlink]: Is a directory in /home/as/public_html/as/wp-content/themes/as/functions.php on line 33
1

how can i add “on focus” do Default Value?

Thanks

http://ww.wp.xz.cn/extend/plugins/visual-form-builder/