Many iPhoto users are having issues while importing pictures. They have reported that at that time of importing pictures from camera to their Mac it says few of the photos will not be imported owing to they are unrecognizable file type or because of the file might not contain a valid data. This very error message indicates that pictures cannot be uploaded as for the reason that their file types are not recognized by the computer.
An alert message appears while importing pictures with the message: "Unreadable Files: The following files could not be imported (they may be an unrecognized file type or the files may not contain valid data)". Whenever you try to attempt to import files this error message pops up. And if the computer hard disk is filled to its limit then it can also pop this error message.
In order to solve the issue of iPhoto errors you can try by following things:
Firstly you need to ensure that the picture files which are importing is actually a picture file or not. You can try to open it with another application. And if possible you can also try this with preview which can easily open the same type of image files that can also be opened with iPhoto. However if the file is unable to open then its likely not a graphic file or probably it is damaged. iPhoto '09 is also perfect in all its features and works greatly.
The "Unreadable Files” iPhoto error message can also pop up when there is no available disk space. So to do the verification of the disk space available go to the strat up disk by selecting the disk icon in the Finder, then select the disk icon, and choose File>Get Info. There you can see the free space available on the disk adjacent to available. If the space available is very less or if the disk is indeed full on the hard disk then delete the files or drag the files which are no longer of use or needed to the trash and empty the trash folder. Also you need to ensure that you make backup of any important files prior deleting it.