I can't find this error in the knowledgebase but we received this error.
It just stated this in the event viewer and essentially told the public the same in the browser.
An error occurred while retrieving your form. Please try resubmitting your request later.
Sure enough, after about 30 minutes, it was ready to go again.
No other errors in the operational or admin log besides this, seems the service just wanted us to wait a bit, but not sure why or how we can prevent this from happening again.
Usually when we receive these specific error codes it is a reference to an article to explain the situation.