What is the actual error message that you are getting, what typs of card is it, and how did the photos get onto the SD card ?
The supported cards are, from http://support.apple.com/kb/HT4101 :
- SDSC
- SDHC
- miniSD
- microSD
- MMC
- SDXC
If you copied the photos onto the card yourself then the card needs to have a DCIM directory on the root of the card with the photos underneath it, and the photo filenames need to be exactly 8 characters long (no spaces) plus the file extension i.e. in a similar format as if a camera had created/written them.