Here's a weird one: we are suddenly getting an AV in a Delphi 5 app that has been running fine for some time against an 8.1.5 database. (DOA 3.4.6.) The message coming back is: A component named DMLQuery already exists. Huh? Looks like DMLQuery is part of DOA's plumbing but we have never seen this one.

We would rather not open up the code on this app if we can avoid it. Any ideas what might suddenly be causing this?

This error is new to me. The DMLQuery component is created dynamically by the TOracleDataSet, but there is only one and it's owned be the dataset, so there cannot be any name clash.

Maybe something goes wrong when the TOracleDataSet is closed? Do you get any other exceptions before this error occurs?

No, no prior errors are shown in our log. And the SQL we were attempting to execute was just a SELECT with one bind variable. Nothing exotic at all. The code is pasted below -- have a look. There's no way to tell from our error log whether it was executing the .Open or the .Refresh when it died. tblResponse is your TOracledataset. If you have any insights we'd be most grateful....
---------------------------------
if Datamodule1.tblResponse.active = FALSE then
begin
DataModule1.tblResponse.DeleteVariables;
DataModule1.tblResponse.SQL.Clear;
DataModule1.tblResponse.SQL.Add(ResponseSQLByEntryID);
DataModule1.tblResponse.DeclareVariable('EntryID', otString);
DataModule1.tblResponse.SetVariable('EntryID', CurResponseID);
Datamodule1.tblResponse.open;
end

else
DataModule1.tblRESPONSE.refresh;

I don't see any problems with this. I don't assume you can provide a (small) demo project that reproduces the issue?