Have you tried resetting the Share(s)?

Below is a more in-depth explanation about the Net Folder feature,
How to use it, and What problems may occur.
http://www.slipstick.com/outlook/netfolders.htm

Outlook uses forms for everything. Perhaps a refreshing of the
forms cache might do the trick.

To do so, follow these steps: 1. On the Tools menu, click Options.
     2. Click the Other tab, and then click Advanced Options.
     3. Click Custom Forms.
     4. Click Manage Forms.
     5. Click Clear Cache.
     6. Close all open windows, and then restart Outlook.

If the above does not work, try the following.

Deleting the Forms Cache File

The Frmcache.dat file is the primary file to delete. The Frmcache.dat
file serves as an index of the individual forms that have been cached
on the computer. Use the following steps to manually delete the
Frmcache.dat file. In addition, these steps delete all of the cached
forms on your computer, which are stored in subfolders of the
Forms folder.

 1.. Quit Outlook.
 2.. Search the Hard drive (<F3>) to locate the Frmcache.dat file.
 (Be sure to check in HIDDEN files on W2K or WXP.)
 3.. Delete all that are found from the FIND window.
 4.. Open Outlook.

When you restart Outlook, and use a custom form, the forms cache
is re-created. Until a custom form is used, Outlook does not re-create
the Frmcache.dat file.

Nikki