On the agent tab -> set credentials page, you have entered a user name with a blank password. When you use the test function, this will always fail.
Although windows does allow blank passwords, and therefore Kaseya allows you to enter a blank password, the test function calls a Windows function to validate that the password is valid on the remote machine. This function does not support the passing of <NULL> as a password, and so the test will always fail.
SOLUTION / WORKAROUND
Do not use / create Administrator level accounts with blank passwords.