MacOS High Sierra 10.13.3

Hello

Entering this commands in Terminal and restarting Mac will help you:

sudo update_dyld_shared_cache

It will ask you for admin Password, Enter your admin password and hit 'Return'.(It will spit out a bunch of "Warnings",Don't be alarmed, It's Normal)

Let it run until it's done.

And then restart your Mac.

Sometimes a simple restart fixes it. Or you can try launching Activity Monitor and typing "pboard" into the search filed. Then choose pboard and use the X at the top left to force quit and try copy/paste again.

Many Users have this problem on Mac Os Sierra 10.13.3 and using pboard does not work for them..

That's true but for some it does, which is why I suggest trying it.