Metadata Problem

I recently bought a new computer and moved the external drive I had used on the old computer. All my photos now have the little exclamation point noting there was an error writing metadata to the photos. The options are to overwrite or retry exporting the metadata. I thought I moved all necessary Lightroom files to be up and running. Did I not move a particular file from the old computer? If not, is there a way to export the meatadata for all the photos at once or do I have to do each one separately (thousands)?