Operating System

Depending on the operating system of the OPC-Server and OPC-Client computer, the user accounts which are used for communication will be identified differently.

Windows 2000

This section describes the required settings for Windows 2000 operating system. On Windows 2000 SP 1, there are some known bugs related to proper callback operation. DCOM servers installed on a Win2k SP1 machine sporadically stop sending callbacks (e.g. OnDataChange) after days or weeks. The error code 0x80010108 (RPC_E_DISCONNECTED) is returned by the DCOM Server when trying to fire a callback. All other calls form the Client to the Server still work fine.

There are three ways to overcome this problem:

release the callback object and subscribe again (recreate the callback object)
install COM + Rollup Package 18.1 (Post Service Pack 2)
install Service Pack 3 (or higher) for Windows 2000

Windows XP

This section describes the required settings for Windows XP operating system only. The default installation for XP forces remote users to authenicate as Guest. This means that DCOM clients cannot connect to a server running on an XP machine unless the Guest account is enabled and has enough rights to launch the server. On the other hand when a DCOM server fires a callback to a remote Client installed on an XP machine, the authentification will be "changed back" to the Guest account (which is mostly disabled by default). Thus, the callback (e.g. OnDataChange) will never get though to the Client. To force an XP machine to "behave" like a Windows 2000 computer the Network Access should be changed to Classic

Open the Security Options dialog with: START >> Control Panel >> Administrative Tools >> Local Security Policy >> Local Policies >> Security Options . Find the following entry: Network access: Sharing and security model for local accounts and change this setting to: Classic - users authenicate as themselves

	In a mixed configuration (e.g. Client installed on XP and Server installed on Windows 2k) the XP machine automatically "changes" to the classic Win2k bevavior when lauching and accessing the DCOM Server, but there will be no callbacks comming through.

Windows 7

This section describes the required settings for Windows 7 operating system only. The default installation for Windows 7 forces remote users to authenicate as "Guest". This means that DCOM clients cannot connect to a server running on an Windows 7 computer unless the Guest account is enabled and has enough rights to launch the server. On the other hand, when a DCOM server fires a callback to a remote Client installed on an Windows 7 machine, the authentification will be "changed back" to the Guest account (which is mostly disabled by default). Thus, the callback (e.g. OnDataChange) will never get though to the Client. To force a Windows 7 computer to "behave" like a Windows 2000 computer, the Network Access should be changed to Classic

Please perform the following steps on the Windows 7 computer:

Open the Security Options dialog with: START >> Control Panel >> Administrative Tools >> Local Security Policy >> Local Policies >> Security Options .
Find the following entry: Network access: Sharing and security model for local accounts and change this setting to: Classic - users authenicate as themselves

	In a mixed configuration (e.g. a client installed on Windows 7 and the server installed on Windows 2000), the Windows 7 machine automatically "changes" to the classic Win2k bevavior when lauching and accessing the DCOM Server, but there will be no callbacks comming through.