I'm developing on a Fujitsu 4120c2 scanner, and acquisition no longer triggers the device event. Even using the acquisition demo (unmodified), and low level twain demo, the Paper Jam event (or any device event) is not thrown. I recall it being triggered before, so why is it not firing now? Also, I can't even set the device event to paperjam, it stays as None.

Thanks.

I don't think that scanner supports device events. 

From the Acquisition demo, select that scanner and then "Capabilities -> Get Supported... -> Capabilities".  If it's a long list you may have to break in the OnGetSuportedItemClick method to see the full list.  If device events is not listed, then the scanner does not support it.

You can also try calling QueryCapability to see if it's supported.