_I experienced this problem after upgrading  under Windows 7 64 Bit with an RME FF400. I reinstalled the RME FF400 drivers (already at the latest driver and firmware release) , re-downloaded the Cubase 6.0.2 update file in case there was a later modification than I had (there wasn't). Without going through all the steps of restoring system images, deleting, updating from 6.0 to 6.0.1 and then to 6.0.2 and also direct from .0 to .2, testing different projects, deleting preference files, unloading and reloading all plugs etc, this is totally solid in that 6.0 is fine, 6.0.1 is fine, 6.0.2 crackles. The Windows performance meters are nowhere near peaking on any of the cores, the VST performance meter is about 1/2 way up, and not a hint of clicks, drop-outs and so on in pre-6.0.2. After the upgrade the VST meter is rhythmically pulsing - I could fix it by increasing ASIO buffer size by a couple of notches (64 to 128 samples), but we're not talking about the odd click creeping in, it's like constant radio interference.

The problem turned-out to be with the vst plugins. Go to your Program Files folder (it will be Program Files (x86) for Cuabase 32 bit in a 64 bit version of Windows. Open the Steinberg folder, open the Cubase 6 folder, open the VST3 folder. There is a file called Cubase plug-in set.vst3. This is updated with each version of C6. 6.0.0 has a file dated 26 Nov 2010 (on my DVD), the 6.0.1 update has one dated 28 Feb 20111 and the 6.0.3 update has one dated 30 Mar 2011. My problem is with the 30 March dated file. Either of the older folders fixes the problem. If you have .0 or .1 installed, copy this file somewhere safe, do the update then replace the newer file.

More details here http://www.steinberg.net/forum/viewtopic.php?f=19&t=8009

_OK - but it still happens.  Search the web and you will find hundreds of people complaining bitterly about bugs and problems.  Sure there are bugs, too many of them, but dig deeper and you will find that many of these problems are caused by hardware incompatabilities, many others by plugins.  There are so-many plugin downloads available that I find myself installing stuff that I don't need almost without thinking about it.  Once installed I'll often open a new toy to see what it looks like and how it sounds in whatever project I'm working on (I know...!) and then forget to remove it (yes, I already  said it, "I know...!"). I recently completed a mammoth and very dull session editing a bass track, saved the project and went to bed. When I went to open it the following morning I got the "Good Morning Andi, you have a Dead Project" message. I tried the old "save under a different name" trick, then I tried the slightly more panicked "backup project to another folder" trick, then the "System Restore just in case" trick, then I made coffee and worked back through the backup files (you know that you can rename a .bak file to .cpr and it will open right?) and found one that opened, but it locked-up if I tried to save an edit of any type.  I opened the mixer and removed all plugins that are not either native to Cubase or that I haven't been using forever and the project saved OK, edited OK and opened OK.  Had I been in a mood to play I  would have removed the plugins one at a time, as it was I just did the lot. Here's the tip - don't add strange plugins to live projects, save a project with a different name BEFORE you add anything at all, and keep a note outside of Cubase of what version is which ( I have well over a hundred versions of some project files).  If you have to revert to a previous version, you may find that you can still open the mixer and channels and plugins and take a screenshot that can allow you to manually re-create settings with minimal effort. Alternatively, remove any new plugins from your plugin folder and open Cubase to allow it to re-scan.  You may find that your project will open but with errors complainig that your new toy can't ber found.