I didn't want to wait until midnight to see if your script worked, so I used the following cron command at the very top of the script:

::cisco::eem::event_register_timer cron name test cron_entry "0 * * * *" queue_priority low nice 1 maxrun 20

I unregistered and re-registered the policy, and even ran the script manually, but it still has not sent an email automatically.  Any thoughts?

Post the output of "show event manager policy registered".

No.  Class   Type    Event Type          Trap  Time Registered           Name

1    script  user    timer cron          Off   Tue Feb 16 19:26:35 2010  sendmail.tcl

name {test} cron entry {27 * * * *}

nice 1 queue-priority low maxrun 20.000

The way you have it registered here, it will run every 27 minute of the hour.  Check the output of "show event manager history event" to see if it's running.  You should also make sure your clock is set correctly (e.g. synced with NTP).  If you still can't get it to run, it would be helpful to see the output of "debug event manager tcl cli" and "debug event manager tcl smtp" after the policy is scheduled to run.

I corrected the clock yesterday by syncing it with an NTP server.  It was only off a little bit.

blmrtr#show debug

Embedded Event Manager:
  Debug EEM Tcl CLI library debugging is on
  Debug EEM Tcl SMTP library debugging is on

blmrtr#show event manager history events
No.  Time of Event             Event Type          Name
1    Fri Feb19  05:00:00 2010  timer cron          script: sendmail.tcl
2    Fri Feb19  06:00:00 2010  timer cron          script: sendmail.tcl
3    Fri Feb19  07:00:00 2010  timer cron          script: sendmail.tcl
4    Fri Feb19  08:00:00 2010  timer cron          script: sendmail.tcl
5    Fri Feb19  09:00:00 2010  timer cron          script: sendmail.tcl
6    Fri Feb19  10:00:00 2010  timer cron          script: sendmail.tcl
7    Fri Feb19  11:00:00 2010  timer cron          script: sendmail.tcl
8    Fri Feb19  12:00:00 2010  timer cron          script: sendmail.tcl
9    Fri Feb19  13:00:00 2010  timer cron          script: sendmail.tcl
10   Fri Feb19  14:00:00 2010  timer cron          script: sendmail.tcl

blmrtr#show log

Feb 19 19:00:01.077: %HA_EM-6-LOG: sendmail.tcl: DEBUG(cli_lib) : CTL : cli_open called.cannot get pty for exec: Error opening vty
Feb 19 19:00:01.077: %HA_EM-6-LOG: sendmail.tcl:     while executing
Feb 19 19:00:01.077: %HA_EM-6-LOG: sendmail.tcl: "cli_open"
Feb 19 19:00:01.077: %HA_EM-6-LOG: sendmail.tcl:     invoked from within
Feb 19 19:00:01.077: %HA_EM-6-LOG: sendmail.tcl: "$slave eval $Contents"
Feb 19 19:00:01.077: %HA_EM-6-LOG: sendmail.tcl:     (procedure "eval_script" line 7)
Feb 19 19:00:01.077: %HA_EM-6-LOG: sendmail.tcl:     invoked from within
Feb 19 19:00:01.077: %HA_EM-6-LOG: sendmail.tcl: "eval_script slave $scriptname"
Feb 19 19:00:01.077: %HA_EM-6-LOG: sendmail.tcl:     invoked from within
Feb 19 19:00:01.077: %HA_EM-6-LOG: sendmail.tcl: "if {$security_level == 1} {       #untrusted script
Feb 19 19:00:01.077: %HA_EM-6-LOG: sendmail.tcl:      interp create -safe slave
Feb 19 19:00:01.077: %HA_EM-6-LOG: sendmail.tcl:      interp share {} stdout slave
Feb 19 19:00:01.077: %HA_EM-6-LOG: sendmail.tcl:      interp share {} stderr slave..."
Feb 19 19:00:01.077: %HA_EM-6-LOG: sendmail.tcl:     (file "system:/lib/tcl/base.tcl" line 50)
Feb 19 19:00:01.077: %HA_EM-6-LOG: sendmail.tcl: Tcl policy execute failed: cannot get pty for exec: Error opening vty

It looks like you may be out of VTY lines.  What version of IOS are you running?

Cisco IOS Software, 2800 Software (C2800NM-ADVIPSERVICESK9-M), Version 12.4(6)T2, RELEASE SOFTWARE (fc1)

line vty 0 4
access-class 99 in
password 7 xxxxxxxxxxxxxxxxxx
login local
transport input telnet ssh
line vty 5 15
access-class 99 in
password 7 xxxxxxxxxxxxxxxxxxxx
login local
transport input telnet ssh

blmrtr#show line
   Tty Line Typ     Tx/Rx    A Modem  Roty AccO AccI  Uses  Noise Overruns  Int
     0    0 CTY              -    -      -    -    -     0      0    0/0      -
     1    1 AUX   9600/9600  -    -      -    -    -     0      0    0/0      -
*  322  322 VTY              -    -      -    -   99   101      0    0/0      -
*  323  323 VTY              -    -      -    -   99    21      0    0/0      -
*  324  324 VTY              -    -      -    -   99    10      0    0/0      -
*  325  325 VTY              -    -      -    -   99     4      0    0/0      -
*  326  326 VTY              -    -      -    -   99     2      0    0/0      -
*  327  327 VTY              -    -      -    -   99     1      0    0/0      -
*  328  328 VTY              -    -      -    -   99     0      0    0/0      -
*  329  329 VTY              -    -      -    -   99     0      0    0/0      -
*  330  330 VTY              -    -      -    -   99     0      0    0/0      -
*  331  331 VTY              -    -      -    -   99     0      0    0/0      -
*  332  332 VTY              -    -      -    -   99     0      0    0/0      -
*  333  333 VTY              -    -      -    -   99     0      0    0/0      -
*  334  334 VTY              -    -      -    -   99     0      0    0/0      -
*  335  335 VTY              -    -      -    -   99     0      0    0/0      -
*  336  336 VTY              -    -      -    -   99    37      0    0/0      -
   337  337 VTY              -    -      -    -   99    20      0    0/0      -

Line(s) not in async mode -or- with no hardware support:
2-321

You are out of VTY lines.  EEM requires at least two VTY lines to be free in order to execute CLI commands.  Try clearing some of the lines, then test the policy.