php 调用指定打印机出错,,,代码如下:

Question

Warning: printer_write() [function.printer-write]: couldn't allocate the printerjobfunction getPrinter($SharedPrinterName) {
global $REMTE_ADDR;
$host = "192.168.0.31";
return "\\\\".$host."\\".$SharedPrinterName;
}$printtest = "^XA";
$printtest = "^F,50^ADN,36,20^FDjoshmoore";
$printtest = "^FS";
$printtest = "^XZ";
$handle = printer_open(getPrinter("Canon LBP2900"));
printer_set_option($handle, PRINTER_MDE, "RAW");
printer_write($handle, $printtest);
printer_close($handle);what's problem?