launchd Job failed to exec(3) for weird reason: 8

I'm trying to schedule a simple task in OS X Mountain Lion 10.8.3

launchctl start nextstopsun.helloworld

command doesn't execute the script and throws a message to a console

4/2/13 9:50:49.663 PM com.apple.launchd.peruser.501[139]: (nextstopsun.helloworld[46729]) Job failed to exec(3) for weird reason: 8

My plist is very simple:

<?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>Label</key>
    <string>nextstopsun.helloworld</string>
    <key>Program</key>
    <string>/Users/nextstopsun/Work/scripts/hw.sh</string>
    <key>StartCalendarInterval</key>
    <dict>
        <key>Hour</key>
        <integer>21</integer>
        <key>Minute</key>
        <integer>15</integer>
    </dict>
    <key>UserName</key>
    <string>nextstopsun</string>
</dict>
</plist>

The script is also very simple

echo "Hello World!" > hw.log

launchctl loaded it with no errors. When executing script from shell it works as expected. Logging off and logging back in doesn't help. Didn't find any answer in Google. Whats that "weird reason: 8" all about?

Few suggestions:

1. Make your script executable (chmod +x <your_script>) or launch it via bash or sh passing script as parameter
2. Most likely: You have error in your shebang line (#!) which cant be recognised by launchd. Try #!/bin/sh or #!/bin/bash. Note that it must be the first line in script.
3. Load your job first via launchctl load <your_plist>. But I think you've already done this or there will be other error message.