SYMPTOMS

When you log on to your mailbox by using Microsoft Outlook Web Access (OWA), you may experience the following symptoms:

• You receive one of the following error messages when you try to use the OWA spell checking feature:
          Message 1
             Unspecified error.
          Message 2
             The spelling in this item can't be checked. Try again later.
• Your OWA session quits unexpectedly.

CAUSE

This behavior may occur if the Outlook Web Access server is published through Microsoft Internet Security and Acceleration (ISA) Server, or if both of the following conditions are true:

• You log on by using only your user alias and password instead of by specifying the domain in a Universal Naming     Convention (UNC) format (Domain\User) or your user principal name (UPN) format ( This e-mail address is being protected from spambots. You need JavaScript enabled to view it ).
• The Exchange virtual server is configured to use forms-based authentication (Cookie-auth).

WORKAROUND

Method 1:

Specify the domain when you log on
When you log on, specify your domain in your logon credentials. To do so, use one of the following formats in the User name list of the Connect to Servername.com dialog box (where domain is the name of your domain, where user is your alias, and where UPN is the user principal name):

domain\user

-or-

user@UPN

Method 2:

Disable authentication for incoming Web requests in ISA Server 2000

If OWA is published behind a server that is running ISA Server, verify that no authentication methods are configured for incoming Web requests.1. Open ISA Server 2000. 
2. Right-click the ISA Server name, and then click Properties.
3. Click the Incoming Web Requests tab. 
4. Select the Web request listener that is used for OWA, and then click Edit. 
5. Click to clear all the authentication methods, including the Integrated authentication method.
6. Click OK.
7. Restart the Microsoft ISA Server Web Proxy service.

Note In ISA Server 2004 and ISA Server 2006, this method must be done on the listener for the publishing rule.