I had two hard drives containing images that I had imported into Lightroom. I wanted to move all images onto the same hard drive. One of the hard drives contained only three folders. With LR open I moved them by clicking on the folder name and dragging it to the other hard drive location showing in the LR Folders list. After closing LR and reopening I discovered that many files in my catalog were missing -- folders on the hard drive I moved the other folders to. When I try to locate the photos I could find them under the main folder where I keep all my photos but when I tried to match them I got the "file is associated with another photo in the catalog" message. I'm not sure how that could be. a search of the two hard drives I was working with came up only one file by that name.
I have looked at the two other questions posed with this same heading and neither answer helped me.
Any suggestions? I do not understand what I may have done that caused so many files to no longer be in their correct location since all I did was drag and drop a folder from the one hard drive to the other where files are now shown as missing that I was not even messing with.