i edited the webassist/ckeditor/config.js file to correct the probelm.
i changed:
config.filebrowserBrowseUrl = "webassist/kfm/index.php?uicolor=eee&theme=webassist_v2&showsidebar=true&startup_folder=cms_files";
to:
if (window.cms_root != null) config.filebrowserBrowseUrl = cms_root+"/webassist/kfm/index.php?uicolor=eee&theme=webassist_v2&showsidebar=true&startup_folder=cms_files";