Internal error: An unexpected error occurred and the operation could not be completed
That is such a general error that without plenty of detail (and likely the logs) it would be difficult to determine what happened. Some of the errors from the Tableau Server are too vague to be of much use.
In that error message there is a sessionID that the Tableau support team will use to track through the logs to link back to the error. Probably not a bad idea to submit a support case if you haven't already. As Toby mentions the error itself is generic and so we'd need to have the log files combined with your screenshot to trace down what happened.