There are many reason possible why the clipboard didn't work. In your case it could be that there are too many copy-actions at the same time respectively too short behind eachother and it might work if you stretched this with WaitForIdle- and/or Sleep-Statements.
For me this problem occured very rarely and the simplest solution is to make a restart from the machine (in earlier days this was a pain but with a quite new machine with a SSD it's very fast). But you could of course also try to clear and/or restart the clipboard.exe respectively search and kill the process which is responsible for, see for example:
How to reset and clear clipboard data in Windows without using third party tools
http://www.walterdevos.be/clipboard-not-working-in-windows-7-internal-error-service-missing
- Marcus
