Missing Record in F9865

Dears i have a custom application with 6 forms (from A TO F)

one of my users wanted to create a grid format on the F form

but he was unable to save it and he gets an error message:

form name is invalid …. please enter a valid form name

i checked the F9865 table and i found 5 records only out of 6 forms whish the app has

form A,B,C,D,E were there in the F9865 table as records

the form F is missing from the table

what could cause this form to be missing and how to create it in the F9865 table