Sending invoice to a buyer, this message comes up: A system error has occurred. Please try again. ??

[123louish123]

When trying to send an invoice to a buyer, this message constantly comes up:

The following critical errors have occurred:

A system error has occurred. Please try again.

What should I do?

[jensmanchester-australia]

This happens quite often - just try again later on. Usually this glitch corrects itself within 24 hours.