Data Controls :: Saving DropDownList Value To Database - Error Converting Data Type Nvarchar To Int

I am using  a  viewstate to store the company Ids and splitting at hyphen.

protected void onCompanychange(object sender, EventArgs e) {
ViewState["companyID"] += companydropdown.SelectedValue + "-";
String companyids = ViewState["companyID"].ToString();
string pattern = "-";
company_array = Regex.Split(companyids, pattern);
company_length = company_array.Length;
}

Company array is a string array  where i have stored the company ids

the problem is company_array[0] has the initial value of the dropdownlist(company) --select company which is why m getting the error(cannot convert data type nvarchar to int) .  I have used the same logic in many places in my project it did not give any error.

int count = 0;
company_length = company_length - 1;
while (count < GridView3.Rows.Count && compid_counter < company_length ) {
cmd = new SqlCommand("insertWorkDetais", conn);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("@trainerId",trainerID);

[Code] .....