Could it be time to patch your ESX Server system?  Hey, at least this is only patch 4 and you aren't having to constantly update your ESX Server with patches like some other systems.  So what do you get with Patch 4?

An updated e1000 driver for additional Intel Pro/1000 based Gig-E cards

Updated VMware Tools (which includes drivers for Red Hat Enterprise Linux 4.0 Update 2.

Fixes for various bugs

The good news, if you haven't updated your ESX Server 2.5.x environment in a while, this patch will upgrade the system to the latest ESX Server 2.5.2 version (if running 2.5. 2.5.1) and it will also update the system with Patch 1, Patch 2, and Patch 3 if they haven't already been applied.

For more notes and installation help, go here.