IrfanView can’t connect to device TWAIN error

I have been using IrfanView for quite some time , and I have found it good and useful. I have the latest version downloaded and installed on my Windows XP machine.
When I try to select some source file I am not able to find anything in the list. It seems to be empty. I try to acquire from the list I get the following error message.
TWAIN error!
Can’t connect to device or the TWAIN driver is not enabled!
Any ideas of why I am not able to find my files in the list?
