Error installing on Ubuntu 14.04

I use a medical imaging system installed on Ubuntu 14.04, before I was able to install ZeroTier with the command
But the last few installation attempts have shown the error:
gpg: key 23E52A61: “ZeroTier, Inc. (ZeroTier Support and Release Signing Key)
gpg: Total number processed: 1
gpg: unmodified: 1
gpg: processing message failed: eof"