Missing icons on files and applications

Hi everyone,

I recently did a complete fresh install of Leopard on my mac pro. One strange thing I have noticed is that some files do not show any preview or icon associated with the file or application. Instead there is a simple dotted outline of a square where the icon would be. The file name below the 'icon' is there but nothing else. Another example is when I copy a file or download a file from a web site. Sometimes when the download or file copy is completed there is no icon above the file name just an empty box outlined with a dotted box.

One other example is when an application is dropped into the applications folder, rather than the applications icon showing up there is a default icon showing two blank documents and a white 'no-entry' symbol.

If I restart my machine or in some cases re-launch finder the icons appear and everything is OK.

Does anybody have any ideas what this could be? I originally had simply upgraded my machine from Tiger to Leopard and I don't recall this being an issue. It has only been after a complete re-install ( hard drive format ) that this problem has started.

Thanks for any help

Allan