Probably, you don't have sufficient access permissions to files and folders.
Please try the following:
- Using FTP, please go to the folder "/public_html/wp-content/plugins/pdf-print"
- Check what permissions are set on the "mpdf" folder (755 must be set for the folder and 644 for files)
- If there are other permissions set, change them.
For more info see Changing File Permissions.