Can't retrieve some photos from Pan...

First, if you want those photos, dont do anything else to the card yet. Use a utilty like RECUVA (you'll find it at http://www.filehippo.com/download_recuva/) it is good at retrieving images from cards in these situations. and better yet its free.

When you are satisfied that all is lost or found...you'll again need to format the card with the camera not the computer. I would also check with the cameras manufacturer website. look for a Firmware update. if one is posted get that and apply it. Some Flash memery cards have advanded features that cameras need updating to handle.

Finally if this keep happending try a new memory card, flash can have defects.
Good luck!