private void tbNuevo_Click(object sender, EventArgs e)
... connections up in the Load....
oCC = new OleDbCommandBuilder(dtc);
DataSet dst= new DataSet();
dtc.Fill(dst, "contador");
iPosact = dst.Tables["contador"].Rows.Count - 1;
DataRow dtr = new DataRow();
dtr = dst.Rows.[iPosact]; //error in this line
vUltimo = dtr["regnum"]; // error in this line


I need to fill the vUltimo with the value of REGNUM in the last record of CONTADOR table. Can help me , please?

dtr = dst.Rows[iPosact]; No . between Rows and [.

You also don't need the new DataRow() part on the line above, you can combine the two lines into

DataRow dtr = dst.Rows[iPosact];


DataRow dtr = dst. don't accept the word Rows after the dot and Intellisense don't have Rows after the dot. Rows word have the error red mark (Say Don't contain definiton of Rows....more...)

dst.Tables["contador"].Rows[blah] ...