Failed to open input stream for file

With the crash of my windows OS, I've moved to Ubuntu recently. All the graphics files used on Picasa/Windows XP are now used on Picasa/Ubuntu. Unfortunately, some of the subfolders did not open. Upon investigating further there are several sub-foldes from the external hard disk that are not being read. I tried launching the graphics files from other applications and keep getting errors such as in the summary above or around permission denied. There is however no difference in the folder permissions. Seems very strange. Please help.