launchd不会为一个用户运行getmail

我已经在我的mac mini服务器上为2个用户启动了使用Lingon的getmail。一个用户的getmail运行正常而另一个用户没有运行。启动项的plist是：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>GroupName</key>
    <string>staff</string>
    <key>Label</key>
    <string>org.intelmini.maggie-mail</string>
    <key>ProgramArguments</key>
    <array>
        <string>/opt/local/bin/getmail</string>
    </array>
    <key>RootDirectory</key>
    <string>/Users/maggie</string>
    <key>ServiceDescription</key>
    <string>Maggies getmail</string>
    <key>StartInterval</key>
    <integer>600</integer>
    <key>UserName</key>
    <string>maggie</string>
    <key>WorkingDirectory</key>
    <string>/Users/maggie</string>
</dict>
</plist>

我从launchd得到的错误是：

Jan 19 08:30:31 intelmini com.apple.launchd[1] (org.intelmini.maggie-mail[7928]): Bug: launchd_core_logic.c:4194 (24498):2
Jan 19 08:30:31 intelmini com.apple.launchd[1] (org.intelmini.maggie-mail[7928]): posix_spawn("/opt/local/bin/getmail", ...): No such file or directory
Jan 19 08:30:31 intelmini com.apple.launchd[1] (org.intelmini.maggie-mail[7928]): Exited with exit code: 1

但是该文件显然存在：

intelmini:~ maggie$ ls -l /opt/local/bin/getmail
lrwxr-xr-x  1 root  admin  71 10 Jan 08:42 /opt/local/bin/getmail -> /opt/local/Library/Frameworks/Python.framework/Versions/2.6/bin/getmail

当我以该用户身份登录时，确实它可以从终端运行：

intelmini:~ maggie$ getmail
getmail version 4.22.2
Copyright (C) 1998-2009 Charles Cazabon.  Licensed under the GNU GPL version 2.
SimplePOP3Retriever:maggie@mail2.gmn-usa.com:110:
  0 messages (0 bytes) retrieved, 124 skipped

是的，所以我不知道如何解决这个问题。运行getmail的用户都是admin。