The issue is that there is a new fonts backend and the old fonts.dat was removed. The installer checks for fonts.data and if its not there, it will give an error. The install actually works I think, but I just tell people to install with RC3 then update to the nightly so they wont complain about the error. At some point somebody should regenerate all the .fir files to not check, but I don't have that capability. The .fir file is the actual hack 'vector' for ML and requires more than basic code knowledge (which is all I have) to generate.