Pen drive does not show on mac on attaching but show error on removal?
If the drive is appearing in Disk Utility and shows up as being mounted, try this:
In the Finder, go to the Finder menu, then Finder Preferences, then General and be sure "external disks" is checked under "Show these items on the desktop". Then on the Sidebar screen and be sure "external disks" is checked under "Show these items in the sidebar."

This should make the drive appear.