Event ID : 1503

Issue : Outlook Mobile Access users cannot access their mailboxes on a heavily-loaded Exchange Server 2003 computer.

Event Source: MSExchangeOMA

Cause : On a heavily-loaded Microsoft Exchange Server 2003 computer, users in your organization may not be able to access their mailboxes by using Microsoft Outlook Mobile Access.
In this scenario, an Outlook Mobile Access user may receive an error message that is similar to the following:
" A system error has occurred, please see your system administrator. "

This problem may occur if Exchange Server 2003 is running on a Microsoft Windows 2000-based computer. In this scenario, virtual memory fragmentation may occur if Exchange Server 2003 is under a heavy load. You may experience this problem during stress-testing of your Exchange Server environment.

Description : An unknown error occurred while processing the current request: Exception of type System.OutOfMemoryException was thrown.Outlook Mobile Access users cannot access their mailboxes on a heavily-loaded Exchange Server 2003 computer.

Action Required : To work around this problem, restart the World Wide Web Publishing service on the Exchange Server computer.

Ref Link:
http://support.microsoft.com/kb/842119/en-us