I have manage to find the problem.I had a method that would take all the courses specific to the value of the combobox and,first of all I deleted the LoadEducation() from the SelectedIndexChanged for combobox and added the method which takes the courses spcific to that education.
private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
this.PopulateCheckBoxes();
}
After,I deleted it(
PopulateCheckBoxes
) from Form_Load because it would have selected the specific courses on top of the ones already there and would have not updated after(that was also one of my problems).I only had the method LoadEducation() in Form_Load() and I deleted it from
private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
.Now it works perfectly for me.Thank you everyone for your help and I hope this could be useful for young developers with the same problem.