Wow.....
So, it turned out that the hardware caused all the trouble!!! And I am very sure about that because I can repeat the flashing if I hold the board (I took my GuruPlug apart) in a certain position. Another hint that it is caused by the hardware is that when the flashing is running and I move the board, I suddenly get errors. When putting the board in the right position again the flashing works/continues. It seems like the JTAG-cable/plug does not give a good connection somewhere. Im not sure where, but somewhere between the JTAG-module and my GuruPlug.
Well I hope thats also the solution for all people which tried to solve it with the timing and JTAG speed and other solutions. I don't even have to press RESET or power on the GuruPlug, the flashing just works!
I tested it on Ubuntu 12.04 and Ubuntu 11.04, with the openocd and everything from here
http://plugcomputer.org/plugwiki/index.php/Reflashing_images_on_the_GuruPlug#Flashing_U-Boot_on_Bricked_PlugTo make it easier finding the right position of the connection, I created a little script which continuously starts the runme.sh and stops after successful flashing.
#!/bin/bash
for i in {1..1000};
do
output=$(sudo sh ./runme.sh ./openocd/uboot.bin)
if [[ "$output" =~ "openocd FAILED" ]]
then
echo ">>> not successful"
echo " "
echo " "
sleep 1
else
echo ">>> done <<<"
echo " "
echo " "
break
fi
done
Just start it in your console from the guruplug-installer directory with
sudo ./run.sh
Well, flashing is actually easy then

mfg