You not only don't need macro sunstitution but it can also cause a problem if priner name has spaces. The Name expression works much better.

...
lcPrinter = thisform.cboPrinter.value
SET PRINTER TO NAME (lcPrinter)
REPORT FORM (lcReport) TO PRINTER NOCONSOLE

>I have designed a custom printer selection form. I have populated the combo box with the printers as follows:
>

>lnPrtCnt = APRINTERS(gaPrinters)
>
>IF lnPrtCnt > 0
>   FOR i = 1 TO lnPrtCnt
>     this.AddItem(ALLTRIM(gaPrinters[i,1]))
>     IF UPPER(gaPrinters[i,1]) = lcPrinter
>        this.Value = gaPrinters[i,1]
>     ENDIF
>   ENDFOR
>ENDIF
>

>
>The print button contains the following code:
>

>lcReport = ???? * name of report that should be printed
>lcPrinter = thisform.cboPrinter.value
>
>SET PRINTER TO NAME &lcPrinter
>
>REPORT FORM &lcReport TO PRINTER
>

>
>However when the SET PRINTER code executes I get the following error:
>Error accessing printer spooler (Error 1957).
>
>if I run this code in the command window
>

>SET PRINTER TO NAME GETPRINTER( )
>

>and then call the REPORT FORM command I dont get an error and the report prints to the selected printer.
>
>How can I get my code to print to the selected printer.