In Outlook, click Detect and Repair on the Help menu, and then click Start. Reboot and then attempt to synchronize.
 

Rename the Mapi32.dll --

1. Quit all running programs.
2. Use the Find feature and search for Mapi32.dll files.
3. Rename Mapi32.dll files to Mapi32old.dll. To do so:
    - Right-click the file name.
    - Click Rename on the shortcut menu.
4. Close the Find dialog box, and then restart Outlook. You might be
    prompted about the changes.  Accept it and hopefully, your problem
    should be solved.

If you encounter any problems then you always have the option of renaming
the files back to their original file name.
 

Reinstall ActiveSync software.  It is recommended to use the latest version available. (Download)
 

I have yet to try this but if you are using Outlook 2003, then try using the command-line switch reference /cleanprofile.  More information about Command-line switches is available here ---

http://office.microsoft.com/en-us/assistance/HP010031101033.aspx

This action is supposed to remove any invalid profile keys and recreates default registry keys where applicable.  This might actually set the profile correct for ActiveSync.  I strongly recommend you perform a backup of your Outlook data before proceeding with this operation.
 

Create a New Profile  and make it point to your old pst file.

Step1 :  Identify the pst file that stores your current Outlook data

If you are unable to locate the path of the .pst file, do the following:

1.  Open Outlook.
2.  Click File -> Data File Management
3.  This should list all the PST files that are present.  Click Open Folder
     and you should find the storage path of your *.pst file.

Example: E:\Documents and Settings\Raj\Local Settings\Application Data\Microsoft\Outlook\Outlook.pst

Step 2:  Create a new Profile

You could try and create a new profile by following the directions and then import the contents into your new profile.  The steps below have been performed on a Windows XP computer.

In Control Panel, double-click User Accounts, and then click Mail-> Show Profiles...

   (Figure 1.)

Then click Add to create a new profile. In this example, I have added a profile called Raj.

  (Figure 2.)

Next double click the newly created profile -> Click Data Files.

  (Figure 3.)

Click Open Folder to view the folder which contains all the PST file and leave this folder open.  Now click Settings to identify the pst file name.

  (Figure 4.)


  (Figure 5.)

Note the filename of the pst.  In this example (E:\Documents and Settings\Raj\Local Settings\Application Data\Microsoft\Outlook\Outlook1.pst)

Close all the profile related windows and return to the following Window:



And configure - When starting MS Office Outlook, use this profile: Choose Always use this profile and select the new profile you created and Click Ok to save the settings.

If you select Prompt for a profile to be used, then when you open Microsoft Outlook it will prompt you which profile should be used.  Now open Outlook and verify if you are able to synchronize successfully.  If the sync is successful, disconnect the mobile device and close Outlook. Then proceed to Step 3 to point the old pst file to your new profile.

Step 3: Rename the pst file

Assuming that you have chosen to save the pst files in the default storage location, both the pst files should be stored in the same path and should be visible in the Windows Folder location that was explained in Figure 4.  All you need to do is rename the old pst file to the new pst.  The shortcut to rename a file is to select the file and then press F2 otherwise right-click the file and then select Rename.

So first rename the newly created Outlook1.pst as Outlook2.pst (this is necessary since you cannot have two files having the same name in one folder) and then rename the old Outlook.pst as Outlook1.pst.  Then rename Outlook2.pst as Outlook.pst so that your old profile has a pst that it can relate to.

Now your new profile will point to your old pst file.

Next Open Outlook and you should be able to synchronize without any problems. Note that if you have any additional pst files in the older profile, then you will need to import them using the File ->Import and Export feature. Once synchronization is successful, then you can proceed to delete the old profile (if any).
 

If none of the solutions work, then the last option is to create a new user account on your desktop with administrative rights on your computer and then attempt to synchronize after logging into this account.  To create a new users on a Windows XP computer --

Click Start -> Control Panel -> User Accounts -> Create a new Account.

Boot the computer and log in as the new user and open Outlook.  This should automatically prompt you with the wizard.  Follow the instructions and once the wizard is complete attempt to synchronize.  If successful, then you have the option of importing the contents of your old *.pst file.