Okay, think I understand EntryHead now. All EntryHead fields (except the autonumber) are duplicated in GeneralLedger. You are using a 5-field compound link on subform. So there will be multiple entries in GeneralLedger for each EntryHead record?
Relationship Builder links are wrong. EntryHead should link directly to GeneralLedger, not through DocumentType.
There is no designated primary key in EntryHead. If you want EntryHead then set its ID as primary key and remove duplicate fields from GeneralLedger. Set the 5 fields in EntryHead as a compound index to prevent duplicates. Save EntryHead ID as foreign key in GeneralLedger. Link the subform on primary and foreign key fields.
Shouldn't CustomerID be in EntryHead table, not GeneralLedger?
Also, Relationship link between GeneralLedger and DcoumentType is wrong - it is not linking with a primary key. Since this GeneralLedger field will be removed, keep link to EntryHead. But either save ID as foreign key in EntryHead or designate DocType in DocumentType as primary key.
Could have a combobox set up to allow input of number or name. It would involve a UNION query as RowSource.
SELECT ID, [Name] AS Data FROM Customers
UNION SELECT ID, ID FROM Customers
ORDER BY Data;
Or have two comboboxes bound to same field and both save the ID.
If I didn't already say - advise not to use spaces nor punctuation/special characters in naming convention.
Also advise not to build lookup fields in table.