I bet you installed 4.1u perfectly. I also imagine that the guide you followed was not so good and failed to emphasize the importance of installing ios60-v6174 to replace the stub ios60-v6400. I also imagine that you don't have boot2 bootmii, so you can't fix it.
You only hope of fixing the wii in the above case would be to use a nand programmer to flash your nand backup back to the wii, if you have one.
At least that is my take on the details provided.