Citrix XenApp: Preventing Explorer.exe from Launching in Shell Mode

Symptoms

• Citrix Presentation Server prevents the Explorer.exe from launching in shell mode.

• Citrix Presentation Server incorporates a new feature which actively monitors whether or not the Explorer.exe is started within a published application and prevents this Explorer.exe from running in shell mode.

• When performing the Search option within a published Internet Explorer, the following message is displayed:

“The system cannot find the device specified.”

Cause

The functions in Windows Explorer: Explore, Open and Search; engage the full explorer shell. Because this call cannot be drawn by a single window, there are two choices:

1) Break out of Seamless mode and present the desktop to the user (see resolution below);

2) Deny the seamless break and let the application calling these functions to generate an error such as the one above.

Workaround

The work around is to disable the CtxHook on Explorer.exe. This enables Explorer.exe to be engaged but it breaks out of the seamless or fixed window session and places the users in a full desktop session.

On Windows 2000 and 2003 32-bit

Unregister the explhook.dll:

regsvr32 /u explhook.dll

-Or-

To disable the hook on the Explorer.exe, edit the following registry key and change the value data to 0.

Caution! This fix requires you to edit the registry. Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Citrix cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use the Registry Editor at your own risk. Be sure to back up the registry before you edit it.

System Key: [HKEY_LOCAL_MACHINESOFTWARECitrixCtxHookAppInit_DLLsSeamless Explorer]
Value Name: Flag
Data Type: REG_DWORD (DWORD Value) Value Data: 6 = Enable Explorer hook (default), 0 = Disable Explorer hook

In Windows 2003 64-bit you are unable to disable the DLL using regsvr32 /u

Caution! This fix requires you to edit the registry. Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Citrix cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use the Registry Editor at your own risk. Be sure to back up the registry before you edit it.

HKEY_LOCAL_MACHINESOFTWAREWow6432NodeCitrixCtxHook64AppInit_DLLsSeamless Explorer
Explorer]
Value Name: Flag
Data Type: REG_DWORD (DWORD Value)
Value Data: 6 = Enable Explorer hook (default), 0 = Disable Explorer hook

Changing this registry key prevents the C:Program FilesCitrixsystem32 explhook.dll from being started. This DLL sets the specific hook on the Explorer.exe.

More Information

CTX991230 – Terminal Server Desktop, Explorer.exe, Launches from a Published Application

This behavior is fully reproducible in RDP when using the Initial Application option.

This has not been reported as an issue in XenApp 5.0 for Windows 2008.

This document applies to:

• Presentation Server 4.0 for Microsoft Windows 2000
• Presentation Server 4.0 for Microsoft Windows 2003
• Presentation Server 4.0 x64 Edition
• Presentation Server 4.5 for Windows Server 2003
• Presentation Server 4.5 for Windows Server 2003 x64 Edition
• XenApp 5.0 for Windows Server 2003 x86

Reference: CTX108784: Preventing Explorer.exe from Launching in Shell Mode