Thumbnails not working / acting very strange

In my 10 years in the field i have never seen an issue like this.

8 desktop pcs ALL experiencing the same issue, all running Windows 7 64bit
1 x Windows Home Server

When the desktop pc's browse any network shares, the thumbnails show for a second then dissapear and you just see blank icons, if you restart explorer.exe they come back for a second, as soon as you refresh, boom they are gone again. In addition to this, if you interrupt the "thumbnail loading" by lets say closing the window. and then try and open my computer, all the shortcuts on the left side of the window are gone, so you can see Favorites, libraries etc, but nothing under that.
If you restart explorer. boom they are all back and work normal, until you browsing network pictures and the issue starts all over again.

Whats strange is that the pictures on the local machine work fine, 100 percent, its only when browsing from the network.

I am almost 100 percent certain it has something to do with the server because my technician took his laptop to the client and it was doing the same thing (but he also had windows 7, just he had 32 bit)

im at a complete loss, can anyone help?

Hi Shawn

thanks for the response. i have tried that with disk cleanup and cc cleaner and no joy.

regards