This problem is a little convoluted, and I'm not quite sure where the root of the problem lies.
I have PRTG running on a Hyper-V VM running Win 2008 R2. This sits on a Hyper-V cluster. It has been running fine for several months. A couple of weeks ago I installed Windows SP1 on both the client and Hyper-V host machines. Since then, the client machine has fallen off the network every 4 days. It loses it's DHCP assigned IP address replacing it with a 169 autoconfiguration IP. The only way I have found to get it's IP address back is a reboot of the VM.
If I try to do a manual DHCP renew with ipconfig /renew it generates an error "An error occurred while renewing interface...An attempt was made to access a socket in a way forbidden by its access permissions" and reverts to a 169 IP. My DHCP lease is set to 8 days, so I'm fairly sure that it's dropping connection after 4 days as this is 50% of the DHCP lease at which point it contacts the server to renew the lease.
I came accross http://support.microsoft.com/default.aspx?scid=kb;EN-US;974909 which provides a hotfix for pre SP1 Hyper-V machines which lose network connectivity when under high network load, so I suspect this may be a related problem. But since the files in the hotfix are considerably older than those in SP1, I'm reluctant to apply the hotfix.
If I disable the PRTG probe service, the problem seems to go away, so I suspect it's the large number of connections PRTG makes (I have a couple of hundred sensors) that's causing the problem.
Has anyone come accross this issue or have a fix?