Naturally I wanted to install this wonderfull component as soon as possible when I began a new project using j1.5.7 this week. Used it non-stop in earlier versions of joomla. Sad to say I got the dreaded message: The ExtJS Library could not be found etc, and the file "fetchscript.php" in the
extplorer directory is not chmodded to 777
(so chmod to 644 or 666)
I've tried all the suggestions that others have put up below but without success.