I'm having problems importing data into a database I have set up for learning SQL and Firebird.

TableA has data in the following fields:
L_Name varchar 30 not null
F_Name varchar 30
DOB Date not null
Gender domain gender, where the domain is char 1, with allowed values of 'M', 'F', or 'U', not null
TableA has no primary key


TableB is empty, and has exactly the same fields plus a primary key:
ID integer, not null, generated by sequence Gen_ID

Below is sql I have used to try to copy data from tableA to tableB:

insert into TableB (l_name, f_name, gender, dob)
select l_name, f_name, gender, dob
from TableA;

When I try running this, the error message I get (I don't know whether from sql or ibexpert) is:

"The insert failed because a column definition includes validation constraints.
validation error for column @1, value "@2".

Firebird 2.5
Win XP SP3
IBExpert personal edition

Thanks in advance for any help you can provide.

Alex