2.6 crashes when IP-forwarding

I am sorry that I can't be more specific now, but I have spent the last several days trying to track down a kernel-panic problem. I first thought it was hardware and I swapped it all out.

System:
1.33 MHz Athlon
Asus mb
1Gb memory
either tulip or 8139too ethernet card.

Symptom: system works perfectly with a ppp dialup until a second machine on the net routes IP requests through the this machine. Then this machine either crashes with a kernel panic or simply locks up completely.

I started with the 2.6 test4 kernel which had been working for several weeks. Then I applied the sequence of patches all the way up to test9. The system was stable with test4 but unstable with test9.

Then I went back to test4 and applied the patches up to test7, and the lockup/kernel-panic problem exists for test7.

Along the way I downloaded all the patches a second time and tried to verify that the downloads were valid. I noted that the patch8 is now different from what it was when I originally downloaded it.