Dan, in an earlier post, gave this reply:
The problem is almost certainly that your system has too many to fit
into the default Windows icon cache. Deleting the cache, or using the
Tweakui repair function may temporarily fix this, but the fix will be
more permanent if you also increase the cache size.
You can increase and purge the icon cache using the free ActivIcons
utility from
http://www.cursorarts.com/ca_ai.html
1-- go to its "Desktop Controls" screen and increase the icon cache
size to at least 2048, and then
2-- rebuild the icon cache. The options for rebuilding the cache are
on 2 small round buttons at the lower/right corner. Shut down any
programs running in the background, then click the round button
farthest to the lower/right corner (your system will reboot, and the
icon cache will be cleaned out).
Or you can increase the cache size by manually inserting a key into
the registry at
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\explorer
here you need to add the key "Max Cached Icons" with a value of 2048
or higher.