http://www.oehelp.com/WMUtil/Default.aspx

NB. People who don't read the short and straight forward instructions
have been known to struggle with it.

Hi Dee,

Give these a try:

*For Outbox & Database problems :

Link for download : '_WMUtil_'
(http://www.oehelp.com/WMUtil/Default.aspx)

1. Close Windows Mail
2. Download WMutil and run it (This is a ZIP file, so be sure to choose
Save rather than Run)
3. Run the wmutil.zip (from where you just downloaded)
4. Extract the two files (Wmutil.exe, scxout.dll) to a folder of your
choice
5. Run the WMUtil.exe (from where you extracted it to)
6. wait a bit until the buttons become active
7. click on Clear Outbox (It may take a while to finish)
IF the buttons will not become active or you get a error message:
(after a minute or so)
A) press Ctrl + Shift + Esc (to open Task manager)
B) click on Processes tab
C) click on WinMail.exe
D) click the End Process button
E) OK any confirmations & rerun WMUtil.exe

Hope it helps,
Shawn

I just worked with a tech - here are the instructions.  They work great.

Windows Mail Cannot Send or Delete Outbound E-Mail

Affected Products: Software
Affected Operating Systems: Windows Vista™

ISSUE: The Microsoft Mail database file is corrupt and does not allow you to
delete sent e-mail. If you try to delete an e-mail, you may receive an error
message "Windows encountered unknown problem page cannot be displayed". If a
corrupt e-mail is in the Outbox folder, no e-mail can be sent.

RESOLUTION: Use the following steps to resolve this issue.
Note: Determine if this issue occurs in only one User account, or in all
User accounts. If this same error happens in other accounts, these steps will
need to be repeated for each account.

Close Windows Mail.
Note: You will need to have your e-mail account information: Username,
password, STMP, and POP3.

Press and hold the CTRL+ALT+DELETE keys. In the menu, click Start Task
Manager.

In the Windows Task Manager window, click the Processes tab.

On the Processes tab, click Winmail.exe, and then click End Process.
View Picture

In the Windows Task Manager dialog box, click End process.
View Picture

From the Windows Vista default Start menu, click Computer.

In the Computer window, from the Organize menu, click Folder and Search
Options.

In the Folder Options window, click the View tab, and then in the Advanced
settings area, under the Hidden Files and Folders section, click to select
Show Hidden files and folders. Click OK.
View Picture

In the Computer window, double-click Local Disk (C:), double-click Users,
double-click the Customer User Account experiencing the difficulty,
double-click Appdata, double-click Local, and then double-click Microsoft.
View Picture

If you wish to save your e-mail, move the Windows Mail directory to the
desktop, or copy the Windows Mail directory to a USB thumb drive. If you do
not wish to save your e-mail, delete the Windows Mail folder. Right-click the
Windows Mail folder, and then click Delete. In the Delete Folder dialog box,
click Yes.
View Picture

Open Windows Mail. All e-mail should now be removed, and the customer e-mail
account will now need to be reset. Windows Mail has now created a new Windows
Mail folder. If you saved the Windows Mail folder, you can copy files back to
the C:\Users\your username\Appdata\Local\Microsoft\Windows Mail\Local Folders
directory.

Close Windows Mail.

From the Windows Vista default Start menu, click Computer.

In the Computer window, double-click Local Disk (C:), double-click Users,
double-click the Customer User Account experiencing the difficulty,
double-click Appdata, double-click Local, double-click Microsoft,
double-click Windows Mail, and then double-click Local Folders.

Right-click the Windows taskbar, and then click Show Windows Side by Side.
View Picture

The side that lists the older dates is the saved e-mail or source data. The
other side is the destination data. Copy or move the files from each folder
you wish to keep. Do not move or copy files with 0 bytes or files that end
with an .fol extension.
View Picture

After moving the files over, open Windows Mail to verify that everything has
been moved over.

Getting similiar problem. Can anyone help?