here is your Corrected code
string strtxt1 = textBox1.Text.Trim();
string strtxt2 = textBox2.Text.Trim();
if (strtxt1 == string.Empty || strtxt2== string.Empty)
{
MessageBox.Show("Please enter something in the boxes.");
return;
}
SqlConnection cnn = new SqlConnection(OMSDB_Connection_String);
string command = "Insert INTO OTM_unsubscriptions (dbPatCnt, dbRespCnt, Email, PracticeID) " +
" VALUES ('"+strtxt1+"','"+strtxt2+"', 1, 1)";
SqlCommand cmd = new SqlCommand(command, cnn);
cnn.Open();
cmd.ExecuteNonQuery();
cnn.Close();
try with above code
Hope it helps