The most likely reason is that the table has no primary key or unique index.
When a table has no way to uniquely identify individual records then dbFront will do it's best to continue functioning but if you attempt to update a row where multiple records might match the update request then it will fail and roll-back the attempted update.
Please open the table properties. If the table is missing a primary key then dbFront will place a warning in the table properties dialog.
Newer versions of dbFront return the message: "No single matching row found".