DNS update callout script always fails.

I have dificult to implement update_dns callout.

When I add a custom_step to my recovery plan and I add script to upgrade DNS It always fails. I get the error:

Warning: The command 'c:\windows\system32\cmd.exe' returned a non-zero value: 1

The strange is, If I execute the script manually from cmd console it works fine, but not throught SRM console.

My questions are:

1.- Which user launch the script.

2.- What type permissions must be in DNS server??

DNS server is a AD 2008 R2

Is there another way to perform this operation??

kinds regards.