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.

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.

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.