PHP exec unable to fork IIS 6.0 -

trying run exec() via:

exec("wkhtmltopdf\wkhtmltopdf fedexdomestic.html fedexdomestic.pdf");

i following error message:

warning: exec(): unable fork [wkhtmltopdf\wkhtmltopdf fedexdomestic.html fedexdomestic.pdf] ...

it works on local server using xampp, not in iis 6.0 server.

i have tried many things work, including following:

1) giving full control permissions iusr in cmd.exe, folder containing .php file, , program i'm trying execute.

2) running cacls %comspec% /e /g %computername%\iusr_%computername%:r via command prompt cmd.exe

3) giving full control permissions network service in cmd.exe, folder containing .php file, , program i'm trying execute (this because read w3wp.exe what's used running external programs, , user name responsible network service).

4) replacing exec() system() , shell_exec()

i have been @ problem days, , have researched , tried many different things no avail.

please help!

got same issue, can't run fuelphp'oil script php script, runing shell directly works , , on local machine works too.