Problem in Picasa

I have just installed Picasa on my dad’s computer so that I can view pictures and post to Facebook etc. I was able to import a block of pictures yesterday (a small percentage of what is on the camera’s memory card). Today I connected the camera to upload some new pictures and all the thumbnails have little red xs in a red circle and the import buttons are greyed out. Selecting pictures doesn’t change the situation.

I have tried uninstalling and reinstalling picasa, as in suggested in their Help. Checking or unchecking "exclude duplicates makes no difference.