This is probably due to an attempt at inserting a new record with a primary key which already exists in the table.
Primary keys for a table can be defined through the primaryKey property on each of the fields in the Database Record. If none are specified, the first field is used.
The error message itself can be suppressed by adding a <Duplicate> exit to the Insert action (right-click on Insert and select it from Add Element), which will cause the model to exit (without inserting data to the database) through this new exit - in this case you should of-course model something to handle this (such as alerting the user or perhaps executing Update instead).
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