Single sign-on feature allows users to go directly from an external user-authenticating application to NetSuite without having to separately log into NetSuite. This feature allows a one-way trust relationship to be established between the external application and NetSuite, so that after users present login credentials to the external application, they can gain access to NetSuite as well.
Currently SmartClient does not support login using SSO; you can try creating a similar role without SSO and log into SmartClient using that role.
We are currently working to enhance the login process with Token Based Authentication and this capability will be rolled out to Enterprise Edition customers soon. With TBA, enterprise licensed users will no more be required to use their credentials to connect their NetSuite Account with SmartClient.