• TWAIN troubleshooting can be divided into two sections:
    • Acquiring the scanner through an ICA session
    • Acquiring the image through the scanning process.

    Section 1: Acquiring the scanner through an ICA session

    1. Ensure that the server edition is set to Advanced or higher.
    2. Ensure that the server version is set to 4.0 or higher.
    3. 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.
    4. 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.
    5. A TWAIN-enabled application must be installed on the server to use this feature. Perform the same test from step 4 on the server console to verify that you can acquire images successfully on the console.
    6. On the ICA client device, ensure that these two files are installed:
      Program Files\Citrix\ICA Client\VDTWN.dll
      Program Files\Citrix\ICA Client\CtxTwnPA.exe
    7. 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.
    8. 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.
    9. Use Filemon to verify the application is looking for Twain_32.dll and what folder it is trying to access it in.
    10. 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):
      Windows 32-bit application: 0×00000008
      Do not substitute user Windows directory: 0×00000400
    11. 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
      : 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:

    • Native
    • Buffered Memory (most scanning software works by default in Buffered Memory mode).

    Notes: 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.

    Section 2: Acquiring the image through the scanning process

    After ensuring the scanner availability through above processes, follow the steps below for proper image acquisition through an ICA session.

    1. Verify if the problem is application specific. Does it happen only to 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.
    2. Try changing different image settings such as color versus grayscale to see if the image acquisition completes successfully.
    3. 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.
      CTX108555 – Hotfix PSE400R01W2k3013 – For Citrix Presentation Server 4.0 for Windows Server 2003
      CTX109090 – Hotfix PSE400R01W2K023 – For Citrix Presentation Server 4.0 for Windows 2000 Server
    4. If this issue is only happening with a 3rd party/custom application, obtain input from the application vendor to determine the process they take to acquire images with TWAIN.
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