Why do I get an black exclamation mark in a black triangle on some of my photos in iPhoto?

Same thing happens to me........can't drag them to the desktop.

Also I cant find a way to empty the SD CARD that loads them onto iphoto

The exclamation mark is an indication that the file path/link to the original file has been broken. Make a temporary, backup copy (select the library and type Command+D) and apply the two fixes below in order as needed:

Fix #1

Launch iPhoto with the Command+Option keys held down and rebuild the library.

Select the options identified in the screenshot.

Fix #2

Using iPhoto Library Manager to Rebuild Your iPhoto Library

Note: This creates a new library based on the LIbraryData.xml file in the library and will recover Events, Albums, keywords, titles and comments but not books, calendars or slideshows. The original library will be left untouched for further attempts at fixing the problem or in case the rebuilt library is not satisfactory.

OT

I have the same problem after updating iPhoto about three months ago. I did the rebuilt a couple of times, but it only restores the thumbnails, which is not your problem. iPhoto does not allow dragging these photos to another location, and the only way I found around this problem is to email the photos to myself to do the manipulation on Photoshop or Preview