And your question is? That's not a lot of info for us to go one. How about giving us info on what , when, who and where for both your machine, system and iPhoto application.
I'll ask a leading question to start the ball rolling: where is this file located that you're trying to import and what is it's file extension?
So sorry...first timer! I have never had a problem with iPhoto...until now. I was loading my pix from my Nikon D90 via usb to iPhoto...it loaded some, rejected 187. That's when I received the following message: The following file could not be imported. The file is in an unrecognized format. Now when I go to RECENT, Last Import, it says there should be 67 photos. There are none. Ugh. I store my pix on an external hard drive...backed up on a time machine G-Drive. Now, every time I try to save upload my photos, I get that message...and then, the request to rebuild my library. I did save them easily to my wife's iPhoto on her mac. No troubles. Any thoughts?
What format is the external? iPhoto needs to have the Library sitting on disk formatted Mac OS Extended (Journaled). Users with the Library sitting on disks otherwise formatted regularly report issues including, but not limited to, importing, saving edits and sharing the photos.
Assuming it's okay, then
Back Up and try rebuild the library: hold down the command and option (or alt) keys while launching iPhoto. Use the resulting dialogue to rebuild. Choose to Repair Database. If that doesn't help, then try again, this time using Rebuild Database.
If that fails:
Download iPhoto Library Manager and use its rebuild function. (In Library Manager it's the FIle -> Rebuild command)
This will create an entirely new library. It will then copy (or try to) your photos and all the associated metadata and versions to this new Library, and arrange it as close as it can to what you had in the damaged Library. It does this based on information it finds in the iPhoto sharing mechanism - but that means that things not shared won't be there, so no slideshows, books or calendars, for instance - but it should get all your events, albums and keywords, faces and places back.
Because this process creates an entirely new library and leaves your old one untouched, it is non-destructive, and if you're not happy with the results you can simply return to your old one.
Try this: launch iPhoto with the Option key held down and create a new, test library. Connect the camera and see if you can import all of the photos into it. If you can then your current library is suspect and you can run the fixes posted by Terence.
Another thing to consider is that the memory card may be corrupted. Once you get all of the photos off the card safely into your iPhoto library reformat the card with the camera just to be sure.