qmail queue problem

Hi,

I have a problem with my qmail server. my domain is netscop.net

so I tried to send an email to a local adresse (webmaster@netscop.net)
from yahoo.com, here is he answser that I gave:

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Hi. This is the qmail-send program at yahoo.com.
I'm afraid I wasn't able to deliver your message to the following
addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

<webmaster@netscop.net>:
66.235.198.107 failed after I sent the message.
Remote host said: 451 qq trouble creating files in queue (#4.3.0)
I'm not going to try again; this message has been in the queue too
long.
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I think that there is a problem with the permissions of the qmail-queue
executable or the queue directory of qmail. because I modified them
manually. Anyone can tell me how they should be?