unable to add data to table because related record is required

I have an access database with my work that I am trying to insert into but I keep getting. > 'You cannot add or change a record because a related record is required in table 'Projects'.' I'm running this query: INSERT INTO Tasks (Assigned,Project,Description) VALUES (@assign,@project,@description) On this Structure: With this code in C# with an OleDb... commands and connections Which are working fine for other query's:

//the assign id is already known and is of type integer.
            string query = "SELECT Project_ID FROM Projects WHERE Project_Name = @project";
            OleDbConnection con = new OleDbConnection(con_string);
            OleDbCommand cmd = new OleDbCommand(query, con);
            cmd.Parameters.AddWithValue("@project", projectComboBox.Text);
            con.Open();
            OleDbDataReader reader = cmd.ExecuteReader();
            while (reader.Read())
            {
                project_id = Convert.ToInt16(reader);
                Console.WriteLine(project_id);
            }
                
            con.Close();

            Console.WriteLine("submit: " + project_id + " " + employee_id + " " + descriptionTextBox.Text + " " + monthCalendar1.SelectionStart.ToString("MM/DD/YYYY"));
            Console.WriteLine(monthCalendar1.SelectionStart);
            query = "INSERT INTO Tasks (Assigned,Project,Description) VALUES (@assign,@project,@description)";
            con = new OleDbConnection(con_string);
            cmd = new OleDbCommand(query, con);
            cmd.Parameters.AddWithValue("@project", project_id);
            cmd.Parameters.AddWithValue("@assign", employee_id);
            cmd.Parameters.AddWithValue("@description", descriptionTextBox.Text.ToString());
            //cmd.Parameters.AddWithValue("@deadline", monthCalendar1.SelectionStart);
            con.Open();
            cmd.ExecuteNonQuery();
            con.Close();
            this.Close();

I have tried looking at other examples of this problem and I don't understand why I'm getting this error. @project has a valid id number of the primary key for a Project, @assign has a valid employee id as well and @description is string of text. Thanks for any help.