After further testing I can see that this might have been a false alarm, sorry.
This problem hasn't occured again.
Tosh McCaber: this seems to be a usable software so I want to ask you something. When I select 'open' in 'file' and select the folder with the pics, how can I drag the mouse cursor over the pics that I want to select, f.ex when I have named all the pictures after an event and want to select the picts without clicking on each one at a time while holding down the Ctrl key ?
Thanks again
Proxus