Hello John Lyon,
Welcome to the MS Q&A platform.
Can you please make sure your IP is in the allowed firewall IP list
When you click on "view details" , do you see the error code details?
In general, if you disable public access to your Azure Synapse Workspace, you will get this error message when attempting to open Synapse Studio.
Here is a Microsoft tech community article explaining this error:
And can you please try manually logging in by going to https://web.azuresynapse.net by selecting your workspace?
also, please check your access to the workspace.
Thisarticle explains how to configure access control in the synapse.
I hope this helps. Please let me know if you have any further questions.