cannot perform this operation on a closed dataset and incorrect data entered into table - sql

Question

I have been getting this error and I am struggling to find what I have done wrong. What doesn't make sense is that the result is still posted to the database with all fields being correct except the name field. In the name field it enters 'dmInfo' for some reason.
with dmQuery_u.dmInfo do
begin
dsInfo.Edit;
qryData.SQL.Clear;
qryData.SQL.Add('SELECT * FROM eventinfo ORDER BY eventnumber');
qryData.Open;
qryData.Last;
autonum := qryData['eventnumber'] + 1;
qryData.SQL.Clear;
qryData.SQL.Add(
'INSERT INTO eventinfo (eventnumber, bandname, venue, dateofevent, ticketcost, openingact, amountbooked)');
qryData.SQL.Add(
'VALUES (:eventnumber, :bandname, :venue, :dateofevent, :ticketcost, :openingact, :amountbooked)');
qryData.Parameters.ParamByName('eventnumber').Value := autonum;
qryData.Parameters.ParamByName('bandname').Value := name;
qryData.Parameters.ParamByName('venue').Value := venue;
qryData.Parameters.ParamByName('dateofevent').Value := date;
qryData.Parameters.ParamByName('ticketcost').Value := ticketcost;
qryData.Parameters.ParamByName('openingact').Value := openingact;
qryData.Parameters.ParamByName('amountbooked').Value := amountbooked;
qryData.ExecSQL;
qryData.SQL.Clear;
qryData.SQL.Add('SELECT * FROM eventinfo');
qryData.Last;
qryData.Open;

Answer 1

Your error is being caused here :
qryData.ExecSQL;
qryData.SQL.Clear;
qryData.SQL.Add('SELECT * FROM eventinfo');
qryData.Last; { !! should be after ---v }
qryData.Open; { should be first ---^ }
Calling .ExecSQL executes a non-query (ie : returns no recordset) command. Since there is no valid dataset here, calling .Last will throw an error. You have to call .Open first.
For the second issue of your name field populating with dmInfo, you're being caught out by use of the dangerous with statement here:
with dmQuery_u.dmInfo do
{...}
qryData.Parameters.ParamByName('bandname').Value := name;
Here the with statement is hiding the name variable you want to use and is instead interpreting it as dmQuery_u.dmInfo.Name. Either get rid of the with statement and use explicit qualifiers for everything or change the name of your name variable.