You cannot use Outlook 98 to customize a contact form that may be used by Outlook 97 users

You receive any of the following errors when working with shared contacts in Microsoft Outlook 97 under the following circumstances:

• When opening an existing contact, you receive the error:
  Can't open this item.
• When creating a new contact item using the first toolbar button, you receive the error:
  The messaging interface has returned an unknown error. If the problem persists, start Outlook again.
• When creating a new contact item using the Contacts menu, you receive the error:
  The form you selected could not be displayed. The messaging interface has returned an unknown error. If the problem persists, start Outlook again.

The contact items are based on a custom form and someone used Outlook 98 to modify the General page of the form.

Do not use Outlook 98 to customize a contact form that may be used by Outlook 97 users. Outlook 98 adds functionality to the contact form and Outlook 97 was not designed to support this added functionality.

In a corporate environment, contacts are often placed in a Microsoft Exchange public folder so that they can be used by everyone in an organization. These contacts often use a custom form to provide functionality specific to an organization.

In general, as with many other situations involving multiple versions of software products, solutions should be created using the earliest release of the product being used in an organization.

For more information about creating solutions with Microsoft Outlook 98, please see the following articles in the Microsoft Knowledge Base: