Symptom:

When you try to list the sources using SourceNameItems property or use SelectSource method to choose a source, you may not find your device in the source list of Dynamic Web TWAIN sometimes.

Causes:

1. The driver of the scanner is not installed.
2. The browser doesn't have enough permission to access the scanner driver.


Resolution:

1. Make sure the driver of the scanner is installed and the scanner is running and properly connected to the machine. You should be able to see the scanner in Windows' Scanners and Cameras Wizard. And you can use Twacker to check if the driver is TWAIN compatible.

2. For IE, please try running the browser as administrator to temporarily elevate the permission level.

For Firefox, Safari, etc., please go to C:\Windows\twain_32 and you should be able to find that your scanner driver has a sub-folder there. In order to show the scanner as an available source, you need to copy the dlls in the sub-folder and paste them to the folder C:\Windows\System32 (or C:\Windows\SysWOW64 on a 64-bit OS).