Message class AM016.
Nothing other this is displayed in help screens also.
Its a standard message and I checked tables for validation rules for my message number , i dint not see any validation rule created for this .
On click of save button , system takes to tax calculation screen and displays this error message.
but I have selected o0 for this which implies zero output tax.
Not sure what config is throwing this error message.
Let me know if this helps.