The chances are that your query was of the form:
INSERT INTO myTable VALUES("Joe", "Bigman" "Smith")
which tries to allocate values on the basis of column numbers: if your auto number field is early in the sequence, one of the given values will be assigned to it - and you will get an error.
Instead of doing that, always name the fields whose values you are supplying:
INSERT INTO myTable (FirstName, NickNAme, FamilyName) VALUES ("Joe", "Bigman", "Smith")
That way, the database knows exactly which column you are trying to insert a value to, and can use defaults or it's own numbers for the remainder. Plus it's a good idea to list the columns anyway, as it prevents data corruption if the table definition is changed at a later date!