During 'Verifying Sage 50 Accounts Login Credentials':
Unable to initialize a connection to Sage 50 Accounts. Sage responded with: Invalid or incorrect username or password.
Check that you're using the correct username and password. You might want to copy and paste the credentials to notepad to ensure it's correct.
Check that the password doesn't exceed the maximum length of 7 characters. If it does - change the password in Sage and retry.