It is very likely there are a bunch of photos in your Picasa photo collection that are displaying the incorrect date and time when the photos were taken. And this isn’t just a problem when your photos won’t sort chronologically. This will also be an issue for you every time you create a new folder or album inside of Picasa and it constantly tries to identify them use the wrong date.
http://www.newstechh.com/blog/How-to-Change-date-and-time-on-digital-picture-taken
http://www.newstechh.com/blog/How-to-Change-date-and-time-on-digital-picture-taken