Details

This message is generated when the indicated argument is not one of the formatting types listed in the value of $BoxForms.
This message can be generated by an incorrect value for the second argument in ToBoxes.
Off[message] switches off the message; On[message] switches it on. For example: Off[General::boxfmt].

Examples

OutputForm is not a valid formatting type for use in ToBoxes:

Valid formatting types for use in ToBoxes are listed in the value of $BoxForms:

This shows valid arguments in ToBoxes:

Top