Most C5 errors are caused by other programs, typically printer drivers. I suggest that you try another driver, at least to see if the problem goes away. Or what about trying to split the function?

cPrinter=SET("Printer",2)
IF PRTINFO(11,cPrinter) < 150

>Hello,
>
>AT one site we are getting error C0000005 in:
>
>IF PRTINFO(11,SET("Printer",2)) < 150
>
>What could be happening?
>
>TIA,
>
>Alex