I had a copy and paste problem but only in two particular Numbers files. A new file is fine, other apps are fine. Deleting the pboard preference didn’t work. These two files also often refuse to open:
[“file name” can’t be opened for some reason.
To open this file, restore it to a previous version.]
Restoring it to a previous version still leaves the copy/paste functions inoperative. Other keyboard shortcuts such as cmd-x and cmd-z seem to work as expected. Other apps work fine. OSX 10.11.6 on iMac 20-inch early 2009 and a Mac Pro 2008.
Suggested fixes on the internet didn’t help so I did some experiments myself. I found that the same files work fine on 10.12 Sierra and it’s newer version of Numbers. The problem persisted on a different account and even after a completely clean install of 10.11 El Capitan.
The fix to copy and paste not working in Numbers for Mac 10.11
I found a fix. It’s not the preferences or the OS, it’s the files itself that are corrupted, even though the same files work fine on my 10.12 (!) they don’t on my Mac Pro 2008 with 10.11.
Here’s the fix: Put the .numbers file back from the time machine / other backup if they won’t open or just open them on a 10.12 Mac. Choose Archive > Export as… and then select Numbers ’09… file. Close the file. The exported file will open and edit without a problem. As soon as you edit it. Numbers asks if you want to convert it to a newer version, just click OK.