Yes, TSScan does support NextGen. There is a little adjustment to be made. On a terminal server you have to delete the following file: C:\Windows\twain_32.dll .
Sometimes Windows caches this DLL and will restore it from its cache: C:\Windows\System32\ddlcache. Delete the twain_32.dll from this location also.
The most common error message assotiated with this issue is: "Unable to close the image device. StartScan: Cannot close Data Source. DG Dat MSG out of expected sequence. Value1:0, Value2:0."