>I have installed PDF Redirect as a virtual printer on a client side.
>On some PC printing to a pdf working fine no matter of default printer,
>but on some pc printing on pdf working only if pdf redirect is default printer. If not,
>when I start printing, message "error loading printer driver" appears.
>
>Any ideas?

Try

declare _fpreset in msvcrt20.dll
=_fpreset()

before changing the printer to PDF printer.