1) Login to your hosting account thru your FTP client.
2) Locate the folder where your Dolphin is installed and go inside "admin" folder.
3) Using your FTP client, change the permissions of ALL files RECURSIVELY to "755".
4) Now try to login to your Dolphin Admin and it should work now. If it still doesn't work, please open a support ticket & our support team will look at the issue.