Drag & Drop freezes in Yosemite

In the last few days my Macbook Pro with OS 10.10.1 has developed a problem with drag & drop: as I try to drag an icon or a group of icons from one location to another, the icons freeze about halfway and then cannot be moved. This has occurred with trying to move single files or folders from one folder to another, also trying to get an app into the dock. It is just the icon(s) I'm trying to move which freeze in place - the cursor doesn't freeze. The only thing that unfreezes the icon is relaunching Finder, but of course this also aborts the move.

So far I have tried: repairing permissions for the hard drive; resetting the P-ram; just putting the computer to sleep for a while. None of these has worked.

Any help would be appreciated.