I am an administrator on SCN.
I see that the account you wrote this message from is a p-user.
Normally when you reset a password for a s-user on Service Marketplace, the new password can be used immediatly to login to SCN.
I am not aware of any issue with this.
if you have multiple user IDs, please verify that the s-user for which you've reset the password on service marketplace is connected to the same SCN account you are trying to login.
If you still believe that there is an issue, contact the support with all the details.