This problem has me really got me pulling my hair out.
My network consists of 16 clients and 1 server, all running Xp Pro. I have them divided into three groups all connected together using three 8 port switches, with one switch getting the internet connection from a D-Link router. I have been using this setup for years without any problem, but my 8 port switches are getting old.
So, i decided to purchase a 24port Edimax switch. Since i want to test it out before doing any major UTP rewiring, i connected the group closest to the router, directly to the 24 port switch (removing their 8 port switch out of the network). then i connected the two other 8 port switches to two ports on the 24 port switch.
i run a ping test on yahoo.com (ping yahoo.com -t) on all the clients and everything seems to be working fine. after a few minutes, one or more will timeout for quite awhile while maintaining local connectivity. i changed to Cnet 24 port, same problem. if i bring back my 8 port, no prob

Not having a lot of experience with Edimax I did have a similar experience with a Netgear 24 port switch. After trying three different units, I switched to a Dlink and haven’t had the issue since!.
What was really strange about all of this is that the Netgears worked just fine in a different location with a different router.?>>? Still confuses me, but that is what occurred. No rime or reason.
Try a different switch. It may just be as simple as compatibility (which you and I know exists even if the manufacturers say it doesn’t!) May be a timing or MTU issue etc but who has time to attempt to really solve it in a real business with an inexpensive switch issue!
Hope that helps
Merry Christmas and God Bless.