Python script is not running under cron, despite working when run manually

I know there have been plenty of questions about this, but I've been trying things for a while with no luck. I have a simple python testscript that creates a folder with a timestamped name. It works perfectly when I run it manually, but nothing happens when I try to put it into crontab. Any idea where I'm messing up here? Here's the script: (located in /home/ec2-user/cronscripts)

from subprocess import call
from time import time
import math

call(["mkdir","derp" +str(math.floor(time()))])

and crontab -l produces the output

* * * * * python /home/ec2-user/cronscripts/testscript.py

I've tried putting 'root' into the command as well, but no dice. I've also tried some to mess around with explicitly setting the PATH variable in the script file.

From root@domU-12-31-38-00-AC-02.compute-1.internal  Wed Jun 15 19:57:01 2011
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Date: Wed, 15 Jun 2011 19:57:01 GMT
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From: root@domU-12-31-38-00-AC-02.compute-1.internal (Cron Daemon)
To: root@domU-12-31-38-00-AC-02.compute-1.internal
Subject: Cron <root@domU-12-31-38-00-AC-02> usr/bin/python /home/ec2-user/cronscripts/testscript.py
Content-Type: text/plain; charset=UTF-8
Auto-Submitted: auto-generated
X-Cron-Env: <SHELL=/bin/sh>
X-Cron-Env: <HOME=/root>
X-Cron-Env: <PATH=/usr/bin:/bin>
X-Cron-Env: <LOGNAME=root>
X-Cron-Env: <USER=root>

/bin/sh: usr/bin/python: No such file or directory

This was the last entry I found in the root mail. It seems to not be able to find python, even though it's exactly where that say it is. And when I print crontab -l, usr/bin/python does have a leading slash. Do I need to change a cron path somewhere?

Use fully qualified path for all commands in crontab.

0 */2 * * * /full/path/to/python /home/ec2-user/cronscripts/testscript.py

Also, all fields are *? When do you expect this to be run? The above example would run every other hr.