All of my images in a catalogue have an exclamation mark in the top right hand corner. I can see the images in Lr but in the develop mode the message reads that the image cannot be found. I recently stripped what I (wrongly) thought to be out of date downloads from my MAC and this is the cause. I have no idea what I removed and have some really important images that I need to work on. Please help a dinosaur.
It seems that you have removed the images. Lightroom is showing the previews that it generated, but the "!" Indicates that the image files are gone. Do you have backups of the images?