This is not addon problem, this is files system permission and file read/writing issue. It may come from some security plugin or from wrong configured file system owners. in any case I recommend delete the addon. Then connect via FTP or cPanel file manager and delete addon folder. The error says WordPress can't fully delete it. S you should delete it manully. Then upload and install it again.
Will this delete my users attachments that they have uploaded? Or will everything just slide back into place like it never happened?