First of all the mailbox you want to access needs to have you added to the permissions list.

See this article for sharing a mailbox, or get the adminsitrator to add the permissions on the server. Once this is done you can attach the mailbox to your profile by doing the following:

Right click on the top of the mailbox tree for your mailbox. From the pop-up list select Properties for mailbox

Click on the Advanced button on the bottom right

Go to the Advanced tab, click on Add.. and enter the mailbox name.

The new mailbox will appear as an extra set of folders below your own mailbox.

Locate( search for files and folders)
outcmd.dat and rename it to outcmd.old. This is a hidden file so you will need to unhide it. This will completely reset the
Toolbar.

No matter we click yes or no, the next time Outlook starts, it gives the same warning message. I found out the problem and writing the solution here for future references.

Why does this occur?

This problem usually occurs with Terminal services installed and running..

When Outlook starts, it creates the following key in registry..
HKEY_CURRENT_USERSoftwareMicrosoftOffice10.0OutlookResiliency (HKCU)
If no problem occurs during startup of Outlook, this key is deleted automatically. Otherwise if an error occurs during the Outlook startup testing, subkeys under resiliency are created and Outlook gives the same warning message as stated above.

If the subkey from resiliency key is deleted by another application, while the terminal server is in install mode, this key gets copied to HKLM (HKLMSoftwareMicrosoftWindows NTCurrent VersionTerminal ServerInstallSoftware\MicrosoftOffice11.0OutlookResiliency)

Now when the application tries to access the key again through Terminal server application mode, if it finds it missing, it looks for the key in HKLM and if it finds TermSrvCopyKeyOnce under Resiliency, it copies the resiliency key again to HKCU.

Now Outlook always looks for the resiliency key and when it finds it, it gives the same warning message.

Solution:

The solution to this problem is rather simple. Only deleting the following key will solve the problem:

HKLMSoftwareMicrosoftWindows NTCurrent VersionTerminal ServerInstallSoftwareMicrosoftOffice10.0OutlookResiliency

When you try to dismiss a reminder in Microsoft Outlook, you receive the following error message:

Microsoft Visual C++ Runtime Library
Runtime error!
Program: c:/…/Outlook.exe
R6025
Pure virtual function call

To solve this problem, start Outlook with one of the following command lines:

“C:\Program Files\Microsoft Office\Office\Outlook.exe” /cleanreminders
-or-
“C:\Program Files\Microsoft Office\Office\Outlook.exe” /cleanviews
-or-
“C:\Program Files\Microsoft Office\Office\Outlook.exe” /cleanfreebusy

If you wanted to open a HTML Message, you may get this error:

“Microsoft Visual C++ Runtime Library (Path to Outlook.exe) Abnormal Program Termination.”

To solve this problem, please deactivate all Addins under:

TOOLS | OPTIONS | OTHER TAB | ADVANCED OPTIONS | ADD-IN MANAGER

After you remove offline items (*.ost files), you may find that it takes longer than expected to synchronize the items that are from the server.

To solve this, please follow the next steps:

Click the Inbox folder, and then press SHIFT + F9 to start a Send/Receive operation for the current folder. This action makes sure that the full item (including the header, the item, and all the attachments that are present) is retrieved.On the Tools menu, point to Send/Receive , and then click Download Headers in This Folder. Restart Outlook 2003

When you try to start Outlook 2003, you may get this errors:

“Outlook.exe caused an ‘access violation’ fault in module riched20.dll at 014f:4802bc95.”

or

“Outlook caused an Invalid Page Fault in riched20.dll.”

After you click OK
Outlook 2003 does not start or Outlook starts and you receive another error message:

“Unable to load “riched20.dll”. You may be out of memory, out of system resources, or missing a .dll file”

To solve this problem follow the next steps:

Rename the riched20.dll
START | SEARCH | CLICK ALL FILES AND FOLDERS | SEARCH Riched20.dll
In the Search Results window, right-click Riched20.dll , click Rename , type Riched20.old , and then press
ENTER

When you try to create a new task you may get this error message:

“Could not complete the operation. One or more parameter values are not valid.”

To solve this problem, please create a new Profile.

Start Outlook 2003
FILE | DATA FILE MANAGEMENT |Add.
Click Outlook 97-2002 Personal Folders File (PST) | OK | OK to accept the default name |OK again
Outlook 2003 now creates a new .pst file that is based on the earlier .pst file and maintains the ANSI formatting for that .pst file
CLOSE | FOLDER LIST
In the navigation pane, you now see the new .pst file
Drag the information from your existing Outlook 2003 folders to the new .pst file
You may also use the Import and Export Wizard on the File menu to move the information from your existing Outlook 2003 folders to the new .pst file
In the navigation pane, right-click the new .pst file, and then click Close “file_name”
Note E-mail messages or other items that contain Unicode characters will not be copied to the new .pst file.

This problem occurs if you use an IMAP profile with Outlook 2003. Outlook 2003′s IMAP support does not support Exchange Client Extensions. Therefore, certain Exchange Client Extensions scenarios do not work correctly when you use an IMAP profile with Outlook 2003