The "Failed deleting" message is a standard Joomla message that is displayed when it does not has the permission to delete a file.
As Joomla does not display the full path, it is hard to tell you where the permission in your environment are wrong.
If you want to know the full path, you need to modify the standard joomla code to display the full path. The source where joomla display this message is
/librarires/joomla/filesystem/file.php
line 216
Something that you may try is to enable the Joomla FTP Layer that sometimes helps joomla to create, update and delete files.
The other "chmod" error in the same filesystem/file.php let me suppose that the path of the file is wrong or that you don't have access.
I strongly suggest that you debug the joomla code and add traces on the "file" to get the full path.
If you don't have the skills to debug joomla, we can do that for you with our billable support that you can order at
www.jms2win.com/en/joomla-multisite?page...35&category_id=1