smrsh: "vacation" not available

Dear Expert,
I'm setting up vacation(1.2.6) program on my email server running sendmail (ver8.13.7) service on Gentoo (2.16.17 ) OS.
Encounter the below "Error1" msg everytime a message send to any users in my sendmaili server, encounter "Error2" msg when send the 2nd time to the same users, how to resolve?

"Error1"
The original message was received at Sun, 10 Dec 2006 21:57:18 +0800
from smtp1.sundomain.com [172.16.0.9]

   ----- The following addresses had permanent fatal errors -----
"|/usr/local/bin/vacation mroot"
    (reason: Service unavailable)
    (expanded from: <mroot@.sundomain.com>)

   ----- Transcript of session follows -----
smrsh: "vacation" not available for sendmail programs (stat failed)
554 5.0.0 Service unavailable
muuygitgnikuy


"Error2"
 The original message was received at Sun, 10 Dec 2006 22:11:58 +0800
from smtp1.sundomain.com [172.16.0.9]

   ----- The following addresses had permanent fatal errors -----
"|/usr/local/bin/vacation mroot"
    (reason: Service unavailable)
    (expanded from: <mroot@.sundomain.com>)

   ----- Transcript of session follows -----
451 4.0.0 putbody: write error: Broken pipe
smrsh: "vacation" not available for sendmail programs (stat failed)
554 5.0.0 Service unavailable
test time date