Epicor 9 system Progress error: A/R block doesn't match caller's; Transaction inconsistency. Epicor Application Event Log

We had this error occur today that I’ve never seen and it actually brought down Epicor. It would not allow anyone to logon after it occurred and I couldn’t access anything. I rebooted the system and it is working again now but was wanting to know if anyone has seen this error before and if so, what might cause it. As stated, our E9 server has been going for 4 years now and this has never occurred so I’d like to figure out what happened.