Jens,
this is since there is no utmr8t.tfm on your system. Older TeX systems had (IMO) wrong tfm file names like ptmr8t.tfm for Times in T1 encoding. The problem is that the "p" means the font-vendor is Adobe, but all font setups have used fonts from URW. Thus the "p" is wrong and has been replaced with the appropriate "u" for URW in modern TeX systems, for example in TeXLive. ConTeXt is correctly configured to use these URW font names. The best solution is to install a TeX system that provides these font names.
Thanks for this, utmr8t.tfm is indeed not on my system at work which is older. I have just installed Gerben's i-installed TeX-fat.dmg on my home machine. It will be interesting to see what is there. I mistakenly thought that I was expecting 8a on the end for ec encoding. I do have ec-utmr8a.tfm manufactured by texfont by type-tmf.dat dated 11/9/01 even thought the overall context is 23/10/02. Appropriate lines duplicated below. # urw times --en=? --ve=urw --co=times --so=auto --en=? --ve=urw --co=times --so=auto --ca=* utmr8a --en=? --ve=urw --co=times --so=auto --sl=* utmr8a --en=? --ve=urw --co=times --so=auto --sl=* utmb8a -- Nigel