While doing F-28 you have to insert bank gl a/c in field 'Account' in 'bank data' section because how can sap can under stand that which gl account should be used for incoming payment. Suppose you have two bank A/C XXX1 and XXX2. Then u will create three GL each for Bank A/C which is as follow:-
1) BANK MAIN A/C
2) BANK INCOMING A/C
3) BANK OUT GOING A/C.
Then how will sap understand to which gl shoul be picked. So pls insert G/L a/c in 'bank data' section .
System will definitely ask you to enter something in the Account field of F-28 but owing to the text of the error message ,it looks like that this is a is customized ABAPED message be and there is a field exit working behind this. In many companies including ours , this is a requirement from audit or finance that this field should be allowed for incoming bank GL Account entry. Hence ABAPER should have implemented field exit for the data element of this field. You may inquire from your ABAPER he will let you know. Incoming bank accounts are designed with special hierarchy e.g starting 3 digitst and end digits should be the same in your all bank GL e.t.c based on this ABAPER implements check so that entry of outgoing or main bank account can ve restricted in this field.