creating a new ODBC user DSN with Delphi

Probably your error or even set of errors is in incorrect translation of ODBC headers, which then may be used for non-Unicode or Unicode Delphi version. For example:

• for Unicode Delphi you rather need to use XxxW (UTF16) functions from ODBCCP32.DLL, than Xxx (ANSI) functions;
• for non-Unicode Delphi rather Xxx functions. And then wideChars should be defined as array[..] of Char;
• SqlConfigDataSource may be defined as XxxW with PAnsiChar;
• etc.

I wanted to show you the idea, because without full sources I can only speculate. Then you have suspicious call StringToWideChar(strAttributes, wideChars, 12);. strAttributes value is much more long than 12 characters.

The following code works well in Delphi XE2:

type
  SQLHWnd = LongWord;
  SQLChar = Char;
  PSQLChar = ^SQLChar;
  SQLBOOL = WordBool;
  UDword = LongInt;
  PUDword = ^UDword;
  SQLSmallint = Smallint;
  SQLReturn = SQLSmallint;

const
  SQL_MAX_MESSAGE_LENGTH = 4096;

  ODBC_ADD_DSN     = 1;         // Add data source
  ODBC_CONFIG_DSN  = 2;         // Configure (edit) data source
  ODBC_REMOVE_DSN  = 3;         // Remove data source

  ODBC_ADD_SYS_DSN    = 4;          // add a system DSN
  ODBC_CONFIG_SYS_DSN   = 5;        // Configure a system DSN
  ODBC_REMOVE_SYS_DSN   = 6;        // remove a system DSN
  ODBC_REMOVE_DEFAULT_DSN   = 7;    // remove the default DSN

function SQLConfigDataSource (
    hwndParent:     SQLHWnd;
    fRequest:       WORD;
    lpszDriver:     PChar;
    lpszAttributes: PChar
  ): SQLBOOL; {$IFDEF MSWINDOWS} stdcall {$ELSE} cdecl {$ENDIF};
  external 'odbccp32.dll' name 'SQLConfigDataSourceW';

function SQLInstallerError (
    iError:           WORD;
    pfErrorCode:      PUDword;
    lpszErrorMsg:     PChar;
    cbErrorMsgMax:    WORD;
    pcbErrorMsg:      PWORD
  ): SQLReturn; {$IFDEF MSWINDOWS} stdcall {$ELSE} cdecl {$ENDIF};
  external 'odbccp32.dll' name 'SQLInstallerErrorW';

procedure TForm616.Button1Click(Sender: TObject);
var
  strAttributes: string;
  pfErrorCode: UDword;
  errMsg: PChar;
begin
  strAttributes := 'DSN=' + 'example_DSN' + Chr(0);
  strAttributes := strAttributes + 'DESCRIPTION=' + 'description' + Chr(0);
  strAttributes := strAttributes + 'SERVER=' + 'testserver' + Chr(0);
  strAttributes := strAttributes + 'DATABASE=' + 'somedatabase' + Chr(0);
  if not SqlConfigDataSource(0, ODBC_ADD_DSN, 'SQL Server', PChar(strAttributes)) then begin
    errMsg := AllocMem(SQL_MAX_MESSAGE_LENGTH);
    SQLInstallerError(1, @pfErrorCode, errMsg, SQL_MAX_MESSAGE_LENGTH, nil);
    MessageBox(0, errMsg, PChar('Add System DSN Error #' + IntToStr(pfErrorCode)), 0);
    FreeMem(errMsg);
  end;
end;