TWAIN troubleshooting can be divided into the following two sections:
Ensure that the server edition is set to Advanced or higher.
Ensure that the server version is set to 4.0 or higher.
Ensure that a version 9.0 or later ICA client is used. Upgrade to the latest ICA client or test downgrading the client to isolate client-side issues.
Test your scanner and application locally by disabling the Windows Image Acquisition (WIA) service. This ensures that only TWAIN is being used for image acquisition.
Perform the same test from step 4 on the server console to verify that you can acquire images successfully on the console.
Note: A TWAIN-enabled application must be installed on the server to use this feature.
On the ICA client device, ensure the following two files are installed:
When you launch the TWAIN compliant application on the server (through an ICA session), use Filemon or task manager to verify CtxTwnPA.exe is being launched on the client workstation when trying to acquire a scanner from the published application. This helps determine if the TWAIN calls are being redirected to the client.
For TWAIN redirection, some applications are not Terminal Services aware and look for Twain_32.dll in the \WINDOWS directory of the user profile (by default, C:\Documents and Settings\UserName\Windows). Copying Twain_32.dll into the \Windows directory of each user profile resolves this issue.
Use Filemon to verify the application is finding Twain_32.dll and the folder in which it is trying to access.
In some instances, the problem can be corrected by adding the application to the Terminal Services application compatibility list with the following two flags specified (see Microsoft Knowledge Base Article 186499 for more information):
To automate the process of enabling these flags on the server, copy the following text to a text editor and save it as a .reg file. [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Terminal Server\Compatibility\Applications\Photoshop] “Flags”=dword:00000408
Note: You might need to combine these flags with other compatibility flags needed for the application.
This feature supports the following modes of TWAIN information transfer:
Buffered Memory (most scanning software works by default in Buffered Memory mode).
The Disk File transfer mode is not supported.
An ICA session from a Win16 or WinCE device (HPC and WBT) does not currently support TWAIN redirection. For additional information on TWAIN redirection support with various non-Windows clients, refer to the client feature matrix at http://www.citrix.com/clientfeaturematrix.
After ensuring the scanner availability through preceding processes, complete the following steps for proper image acquisition through an ICA session.
Verify if the issue is application specific. Does the issue occur only for a custom application or all the applications on the server? The Microsoft Image Scanning utility is a useful tool for verifying the image acquisition process.
Change different settings of the image, such as color versus grayscale to see if the image acquisition completes successfully.
Known Issue: When using TWAIN redirection, third-party published scanning applications might unexpectedly exit while receiving scan data from the client. This issue is limited to scanning in grayscale mode.
Refer to CTX108555 – Hotfix PSE400R01W2k3013 - For Citrix Presentation Server 4.0 for Windows Server 2003 and CTX109090 – Hotfix PSE400R01W2K023 - For Citrix Presentation Server 4.0 for Windows 2000 Server for more information.
If this issue is occurring only with a third-party or custom application, obtain input from the application vendor to determine the process taken to acquire images with TWAIN.
CTX123981 – How to Get TWAIN to Work in XenApp 5.0 for Windows 2008 32-bit or 64bit
CTX107059 – Advanced Concepts Guide for Presentation Server 4.0
CTX107409 – TWAIN Redirection Support with XenApp FAQ
CTX106765 – Explaining Scanner Support with Citrix MetaFrame
CTX117445 – Some TWAIN enabled applications may appear to hang as dialog boxes can not be closed
CTX108392 – TWAIN Redirection Does Not Work Properly When Using Web Client Version 9.x
CTX118357 – The CtxTwnPA.exe Process Crashes while Trying to Acquire an Image on Windows Vista 64-bit Using a Xerox DocuMate 510 Scanner