That would suggest that the following file is missing or unreadable. Can you find it on your server?
library/Zend/Mail/Transport/Sendmail.php
It's worth bearing in mind the file permission errors you had previously. If the file is there, it's likely unreadable so you may need to consult your host for assistance here or adjust the permissions again.
If the file doesn't exist, I would suggest downloading the files again from your customer area and re-uploading them all. Pay attention for any files that have failed (some FTP clients don't make it ever so obvious that files have failed) and any reasons logged for those files failing.
If you continue to get the errors after this, do the same again but use a different FTP client.