I received this error and support was able to fix it on the server side: Case number: 113050610417883
I was told this occurred because the account listed as the main billing account on Office 365 was not used to create the CRM account. I have 2 global admin accounts defined and used the other one.
Note that CRM login would work for the main global admin. This error only occurred for the account used to create the CRM trial.
Also note that accessing the site directly (at domainname.crm.dynamics.com) will provide a different error about the login account.