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Unable to Scan in a Terminal Services Environment

Document ID:SO4683

Usergroup :External


Cannot select scanner or digital camera; Cannot insert image; Network TWAIN not working; Terminal services scan; Scanning failure in Citrix; Image acquisition not possible; Scan failure


Citrix metaframe; Terminal Services; Scan to network; Scan to PC; Scan to profile


What you will see


Unable to scan in a Terminal Services environment.


Article Contents


NOTE: Make sure your Lexmark MFP supports local and network TWAIN before reading or attempting any of the suggested remedies found within this article.  


Terminal Server Modes

Before suggesting a remedy, it is important to know what terminal service mode is being utilized in your workplace:

Remote Administration Mode

Remote Administration mode is equivalent to Remote Desktop Connection and, as its name implies, is for servers administering from a different physical location.


Application Server mode

Application Server mode serves applications to users from a central server.

Click here for more information for Microsoft's white paper about terminal service modes. 


Why does scanning fail?

First, in Application Server mode, each user gets their own copy of the Windows directory, by default C:\Documents and Settings\UserName\Windows.

NOTE:  The TWAIN Data Source Manager (DSM) and the vendor-supplied TWAIN data sources are typically installed in the <Windows Drive (Letter)>:\Windows directory and not the above-mentioned "user" directory

Scan failure decision table


If... Then... And...
Your TWAIN application is Terminal server-aware

the application will know to look in the "user's" Windows directory for the TWAIN DSM

user's = UserName

You may still need to perform a redirect depending on your Terminal Server version. See Suggested Remedies below.
Your TWAIN application is not Terminal server-aware the application will not know to look in the "user's" Windows directory

the TWAIN application will be unable to load the TWAIN DSM.

See both Suggested Remedies below.



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 Suggested Remedies

Try one or both of the following:

  1. The TWAIN DSM (twain_32.dll) and DSM can be copied into the user’s Windows directory.

To do this, copy <Windows Drive>:\Windows\twain_32.dll and the entire <Windows Drive>:\Windows\TWAIN directory into C:\Documents and Settings\UserName\Windows, or equivalent directory. 

  1. Redirection by performing a registry change that prevents the application/operating system from substituting the "user’s" Windows directory for <Windows Drive>:\Windows.

Registry change example: [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Terminal Server\Compatibility\Applications\<Application Name Here>] “Flags”=dword:00000408

Important! Lexmark is not responsible for assisting users with this procedure.

To help assist with this procedure, click here to see Microsoft's Knowledge Base article ID#186499; or click here for Citrix's Knowledge Base article ID#7767.

NOTE: The application flags must be combined with any previously exiting application flags, otherwise the old flags will be overwritten.




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General Terminal Services Scan Support Table

Scanner Connection Scan Method Scan Permitted?
Local (USB) connection to the Terminal Services client PC (TWAIN)

Yes. However, only Citrix Presentation Server 4.0 provides such a redirect feature for TWAIN drivers.

How does this work? The redirection component enumerates TWAIN drivers on the Terminal Services client PC, and makes those TWAIN drivers appear as if they are installed on the Terminal Services server.

When a scan is performed, the image is redirected from the client PC to the server.

Local (USB) connection to the Terminal Services client PC (WIA) No redirection exists for WIA scan drivers.
Local (USB) connection to the Terminal Services server PC. (TWAIN) No, this unlikely scenario is seldom considered because users will probably not be in the same physical location as the Terminal Services server PC.
Network connection of MFP. (Network TWAIN)

A redirect feature is not required because the MFP can be accessed directly from both the Terminal Services client and server PCs.

Therefore, Lexmark’s Network TWAIN solution is natively supported in most Terminal Services environments.

NOTE: The TWAIN driver must be installed on the Terminal Services server PC. 

Citrix Presentation Server 4.0 – If TWAIN redirection is enabled, the TWAIN driver must be installed on the client PC. Again, the TWAIN driver on the client will be redirected to the server.




Related Articles

The option to select scanner or digital camera is grayed-out; i.e., indicating it is not operational. 

Click here for a Microsoft article that explains why Microsoft Office products may not support TWAIN devices in environments with multiple concurrent scanner connections and multiple users. 




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Contacting Lexmark 

Please contact Lexmark if you need additional support assistance. NOTE: When calling for support, you will be asked for your MFP machine/model type and serial number (SN).

Please call from near a computer and printer in case the technician on the phone asks you to perform a task involving one or all of these devices


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