WP-SpamShield changes a default behavior of WordPress, which MarsEdit relies upon when connecting to your blog. Normally, if an incorrect or empty username and password are provided, WordPress responds with a request to prompt the user for a password. WP-SpamShield changes this behavior so that WordPress’s usual response is not delivered.

To work around this problem, you need to manually enter your username and password into MarsEdit:

1. Click the blog’s icon in the main MarsEdit window.
2. While holding the Option key on your keyboard, click the Blog menu at the top of the screen, and select “Enter Password”.
3. Carefully retype your correct login and password.

Now when you refresh the blog again, it should connect without prompting and without presenting an error.