If you met login errors in excel addin, please follow the steps list below to trouble shoot your problem.
1: options -> KSP Server->
Verify you have correct KSP cloud server, https://kspv2.microsoft.com/ServiceContainer
and verify you typed correct adCenter Username and Password.
2: Test your login in https://adCenter.microsoft.com
you must have a valid and activated adCenter login to be able to use adCenter Excel addin.
3: Verify your machine's system clock is correct
adCenter Addin need to encrypt all communications using your time information. Please make sure your system clock is accurate (within 5 minutes), and please check if you have summer saving time correctly set.
4: Check your Router/Firewall to see if it blocks communication from Excel to https://kspv2.microsoft.com
(One of our customers solve the issue by upgrade the router's firmware.)
5: If you still can not get the login working, please mail your login/password to adSage@microsoft.com, so that we can help you try it in house.
Thanks,
Dylan Huang
Microsoft adCenter Keyword Services Platform and adCenter Excel addin