I reinforce the comments from Tumbleweed with respect to the use of registry cleaners.
However, with respect to your PS CS4 problem the only thing that I suggest is checking your scratch disk setting in PS Edit-->Preferences-->Performance. If you can, set up the scratch disk on a different drive to the one that the programme is on.
I have been using Photoshop for many years but have never seen this particular problem before. Please let us know how you resolve it.