Some versions of PHP like mine have a problem with the php function realpath. Its a buggy function and for this reason some users experiment a frustration beacuse the visual editor included with wordpress (tinyMCE) is not working properly. The small editor toolbar does not appear when you want to create or modify a document and the visual editor option is activated for the user.
I modified the file tiny_mce_gzip.php and I send it to you. The new substitution function is call real_path and is a copy of an example that appears in www.php.net.
I hope this report is usefull for every wordpress user and as a suggestion I think that in future releases of this gorgeus blog software it could be appear in the administration panel a checkbox in Options->Write with the subject "buggy realpath function". If you check this option wordpress will use an alternative function.