There's a faq that discusses exactly the same problem.

>Update.....
>
>Ignore this, moments after posting I went into the frx and cleared the Tag and Tag2 fields.
>Guess what, It worked :)
>
>End Update....
>
>
>
>Hi all,
>
>I have a strange occurance happening, I am currently in VFP 6, I have not looked at it in 7 as of yet.
>
>We do some printing to PDF files using the Ayumni (sp?) PDF Drivers.
>But it seems to quite frequently print to the wrong printer.
>
>I have 3 printers installed at this point
>OfficeJet
>LaserJet
>PDF (created by Ayumni at runtime)
>
>OfficeJet is set to default, and before starting the app SET("Printer",3) returns OfficeJet.
>
>an exmaple of some code from the command window at run time just before printing.
>This is after having issued SET PRINTER TO NAME "blah" and all that.
>

>?SET("Printer",3)
>=> PDF
>?SET("Printer",2)
>=> OfficeJet
>sys(1037)
>=> Default selected is PDF
>report form (this.cFrx) to printer prompt noconsole
>=> Default selected is LaserJet
>=> Prints to LaserJet
>

>
>I have Done APRINTERS() and all the printers appear in there fine, and if I have 'prompt' in the print command and selected the PDF file, it prints to that.
>
>Any ideas?