zypper checksum errors

I tried the live upgrade from 11.1 to 11.2. After “zypper in zypper”, I got lots of random checksum problems. It was practically impossible to get the big packages. So I downgraded zypper and now it is OK, but I abandoned the “dup” distro upgrade.
In fact I had already this problem earlier when I upgraded zypper from the factory repository. But there is no problem with another rpm based distro. Also earlier I had a similar problem with apt-get/deb systems, but strangely the latest release works without any problem.
HW: Intel DQ963FX MB with integrated GMA 3000 video, Intel D440 CPU, 2x512 MB DDRII 667 MHz RAM (Corsair)

Any idea? As the distro upgrade has been interrupted but several packages have been removed already, I had a broken 11.1 install after restart. Of course, I could use the 11.2 install DVD for the upgrade, but if zypper is not going to work I see no point in that. 11.1 worked well with my HW.