I figured out the problem, but I don’t understand it – My proxy settings were fine (51 kept the old config info, as it should). The problem was that I had to select the “compatible” box in the “Valid updates” section of Install/Update in order to install 5.1 as an upgrade to the 5.0 install. After that the updates didn’t work until I re-selected the “equivalent” box. This is not MyEclipse’s problem, but more appropriate error messages would certainly help here!