Why could CreateFile fail on a network drive - delphi

Question

I have one installation that behaves VERY oddly... Every time we try to copy something on a network drive we check accessibility with code like this:
procedure TForm1.TestAccess;
var fn : string;
hdl : THandle;
res : boolean;
dir : string;
flags : Cardinal;
begin
dir := edDir.Text;
flags := FILE_FLAG_DELETE_ON_CLOSE or FILE_FLAG_NO_BUFFERING or FILE_ATTRIBUTE_HIDDEN;
fn := FindUnusedFileName( IncludeTrailingPathDelimiter( dir ) + IntToStr( Random(10000) ) + '.tst' );
memLog.Lines.Add('Try to create file: ' + fn);
hdl := CreateFile( PChar(fN), GENERIC_READ or GENERIC_WRITE, FILE_SHARE_DELETE, nil, CREATE_NEW,
flags, 0 );
res := hdl <> INVALID_HANDLE_VALUE;
if not res then
begin
memLog.Lines.Add('Error: ' + SysErrorMessage(GetLastError));
end
else
memLog.Lines.Add('Success');
if res then
CloseHandle(hdl);
end;
where memLog is a TMemo and edDir is simply an edit field.
Now here is the strange part... I get an access denied on that system meaning uploading will fail most of the time (most of the time is the strange part here).
Another thing is that in a first attempt I used the JvDirectoryEdit control. In that case the result is twofold... If I enter the directory (UNC Path) there without a backslash I get the access denied too. If I enter a final backslash and the combo box window pops up showing the content (aka directories) in that folder it finally works!!!
So... First: has anyone a clue what the problem might be and do I something wrong here?

Answer 1

I have used this procedure in the past to check if a directory is read-only, maybe it can be useful:
FUNCTION DirRO(NomeCartella : String) : Boolean;
VAR VarFile : TextFile;
NomCart : String;
BEGIN
Result := False;
If NomeCartella[Length(NomeCartella)]='\'
Then NomCart := NomeCartella
Else NomCart := NomeCartella+'\';
Try AssignFile(VarFile,NomCart+'^ghi.kol');
{$I-}
Rewrite(VarFile);
{$I-}
If IOResult<>0 Then
Begin
Result := True;
Exit;
End;
CloseFile(VarFile);
Erase(VarFile);
Except Result := True;
End;
END;