The symbol means you do not have permission to access that volume. How did you format the drive? Also, you should be copying (“cloning”) your data instead of drag-and-drop. I recommend Carbon Copy Cloner, or you can use Terminal, if you are familiar with the commands.
If you really have to fix access to that drive, select that drive in Finder and then Get Info. You will have to click on the padlock (lower left of the window) and select admin and/or everyone and change Privilege to Read & Write. In the small pulldown at the bottom, you may have to also select Apply to enclosed items… This assumes that you are logged in as Admin.