Sorcha –

If your techie is still puzzled, you may want to inform him that the MaxCachedIcons key change I described from PC Magazine is an "officially documented Microsoft fix." Mickey'$ Knowledgebase articles are rather "terse," as in "we don't really like to have anyone know this is a problem," but I believe you will find your difficulty described in Knowledge Base article:

132668: Icons Randomly Change to Different Icons

And in article:

133733: Icons Displayed Incorrectly in Control Panel

Default cache size is 500 – if no key is present in the registry. The maximum size is 4096 officially, although a couple of "bootleg" sites suggest it can be set higher. The DWORD value 4096 should be more room than you're likely to need.

These are fairly old articles, and possibly the reason they were so hard to find is that Mickey'$ search engine looks in "recent" hit lists first. Judging by the number of hits in the outside world, it's actually a pretty "popular" problem, although I'd not seen it before.

John