If the memo file is too full to add the new memo pad to, INMEMO will display the appropriate error message on the bottom of the screen and require the operator to hit RETURN to proceed. INMEMO will then return to the calling program in the normal fashion, except that it will set POS to MMO'FUL (1). The program should have some sort of error recovery to process this and all other INMEMO errors:

XCALL INMEMO,MMO'EDT,...

IF POS <> 0 CALL INMEMO'ERROR'RECOVERY

Note that you can use EXPMMO to expand the memo pad. Also note the use of XPOS and POS - see the parameter definition of XPOS:  Return status codes for more details.