Null Exception Error With ComboBox

[polymorphic]

Error: "Object reference not set to an instance of an object"

I have a ValueMember set for a comboBox and I am wanting the value of the ValueMember for the selected Item. This is c# VS2005.

I do not understand why I am getting this error with the code below:

private void cboFindEst_SelectedIndexChanged(object sender, EventArgs e)
{
if (cboFindEst.SelectedIndex != -1)
{
string sID;
sID = cboFindEst.SelectedValue.ToString();
fillDataSet(sID);
}
}

Does anyone have an idea?

Thanks,
cj

[polymorphic]

I fixed this. Because I was populating the comboBox via code, the data was never binding correctly so I broke down and used a bindingSource.