hmm... well I've fixed it. it seems kind of odd, though.
I have a 3Com 3C940 inbuilt ethernet controller. Now some say 3c2000.o must be used as a driver for this card, and some say sk98lin.o can be used too. Now when I use 3c2000 (which seems to be the right choice, because it is even supplied with my motherboard), I get contact with my modem and all seems fine, but dhcp doesn't seem to work and therefore no ip. so in a way i didn't even connect and that is why I got those errors.
Now if I 'rmmod 3c2000', bring down connection with 'ifconfig eth0 down' and then 'insmod sk98lin' instead and bring network up again by 'ifconfig eth0 up' everything works in an instant.
must be something wrong with the 3c2000 driver....
but well , anyway, it's fixed now