When configuring the plug-in, does the test succeed when you used the Test button?  How long does the sync work before you get Session ID?  What is the exact text error message?

Can you login to the SplendidCRM app and check the SystemCheck.aspx page for errors.

Once you get the Test button to work, you should not see the invalid SessionID error for 20 minutes as it takes that long for the ASP.NET session to timeout.  If you see the SessionID earlier, then it suggests a different problem, possibly the web server restarting.

If you are using Windows Authentication, then the answer is yes as we create the new user account the first time you visit the site.  If you are using SplendidCRM authentication, then you do not need to visit the site first because your account must be manually created.