Problem after upgrading udev and kernel

I have upgraded to kernel 2.6.15.4  (archlinux build) and after being 
connected for like 30-60 mins, my PC suddenly becomes very slow and the 
connection drops : (i'm using linuxant hsf 7.43.00.01)

This is what I get in my /var/log/messages.log

Feb 12 12:22:56 darkstar pppd[3394]: No response to 4 echo-requests
Feb 12 12:22:56 darkstar pppd[3394]: Serial link appears to be disconnected.
Feb 12 12:22:56 darkstar pppd[3394]: Connect time 61.6 minutes.
Feb 12 12:22:56 darkstar pppd[3394]: Sent 632818 bytes, received 5086832 
bytes.
Feb 12 12:23:02 darkstar pppd[3394]: Connection terminated.
Feb 12 12:23:06 darkstar pppd[3394]: Modem hangup
Feb 12 12:23:06 darkstar pppd[3394]: Exit.


Note my kernel is compiled with:
PKGBUILD                             emu10k-suspend.patch        
logo_linux_clut224.ppm              sata-suspend.patch
acpi-dsdt-initrd-v0.7d-2.6.12.patch  ipw2200-monitor.patch       
ndevfs.patch                        uevent-2.6.15.patch.bz2
acpi-fixup.patch                     kallsyms-compression.patch  
powernow-k7.patch                   usb-input-fix.patch
config                               kernel26.install            
sata-enable-atapi-by-default.patch  vt8231-new-driver.patch

I tried the options noapic, pci=noacpi, but nothing changed.
I'm using the free version of HSF.

Thanks in advance for your answers

Denis