If you're playing on a Trial Account, Mythic has these words for you:

We're currently working to correct an issue that can cause Trial account players to be incorrectly notified that they must upgrade their account when attempting to login to the game during server downtime. If you receive this message but your 10 day trial has not yet expired this is most likely the case.

We realize this message can be confusing and apologize for any inconvenience it has caused, we will have it resolved as soon as possible. If you receive this message and the servers are not offline please check the status of your account in the Mythic Account Center to check the status of your trial and contact Billing/Technical support if you require further assistance.

My opinion?  Just buy it!  You'll be glad you did.