I finally found the reason why was unable to generate the format. It is a luatex bug. First the report (which I had prepeared before discovering the cause).
I have experienced the same problem both under Windows (XP) and under Linux (Ubuntu), and not only with lmr fonts but also with cmr10; and with any version I have tried since the one from TeXLive 2008.
Here are the last lines of output with kpathsea-debug=-1 for LuaTeX and the corresponding ones for PdfTeX, as well as the relevant lines from texmf.cnf. Although the directory is named texlive2007 the executables are from texlive2008.
LuaTeX:
kdebug:fopen(/usr/local/texlive2007/texfm/fonts/map/fontname/texfonts.map, r) => 0xcb5590
kdebug:fclose(0x8cb5590) => 0
kdebug:hash_lookup(ec-lmr12.ofm) => (nil)
kdebug:hash_lookup(ec-lmr12) => (nil)
kdebug:hash_lookup(ec-lmr12.tfm) => (nil)
kdebug:hash_lookup(ec-lmr12) => (nil)
kdebug:start search(files=[ec-lmr12.ofm ec-lmr12.tfm], must_exist=0, find_all=0, path=!!/usr/local/texlive2007/texfm/fonts).
kdebug:hash_lookup(ec-lmr12.ofm) => (nil)
kdebug:hash_lookup(ec-lmr12.tfm) => /usr/local/texlive2007/texfm/fonts/tfm/public/lm/
kdebug:start search(files=[ec-lmr12.ofm ec-lmr12.tfm], must_exist=1, find_all=0, path=!!/usr/local/texlive2007/texfm/fonts).
kdebug:hash_lookup(ec-lmr12.ofm) => (nil)
kdebug:db:match(/usr/local/texlive2007/texfm/fonts/tfm/public/lm/ec-lmr12.tfm,/usr/local/texlive2007/texfm/fonts) = 0
kdebug:search([ec-lmr12.ofm ec-lmr12.tfm]) =>
! Font \twelverm=ec-lmr12 not loadable: metric data not found or bad.
<to be read again>
PdfTeX:
kdebug:fopen(/usr/local/texlive2007/texfm/fonts/map/fontname/texfonts.map, r) => 0x83491e8
kdebug:fclose(0x83491e8) => 0
kdebug:hash_lookup(ec-lmr12.tfm) => (nil)
kdebug:hash_lookup(ec-lmr12) => (nil)
kdebug:start search(files=[ec-lmr12.tfm], must_exist=0, find_all=0, path=.:!!/usr/local/texlive2007/texfm/fonts/tfm//).
kdebug:kpse_normalize_path (.) => 0
kdebug:kpse_normalize_path (./ec-lmr12.tfm) => 0
kdebug:hash_lookup(ec-lmr12.tfm) => /usr/local/texlive2007/texfm/fonts/tfm/public/lm/
kdebug:db:match(/usr/local/texlive2007/texmf/fonts/tfm/public/lm/ec-lmr12.tfm,/usr/local/texlive2007/texmf/fonts/tfm//) = 1
kdebug:search([ec-lmr12.tfm]) => /usr/local/texlive2007/texfm/fonts/tfm/public/lm/ec-lmr12.tfm
kdebug:fopen(/usr/local/texlive2007/texfm/fonts/tfm/public/lm/ec-lmr12.tfm, rb) => 0x834e418
kdebug:fclose(0x834e418) => 0
kdebug:start search(files=[ec-lmr12.ofm ec-lmr12.tfm], must_exist=1, find_all=0, path=!!/usr/local/texlive2007/texfm/fonts).
kdebug:hash_lookup(ec-lmr12.ofm) => (nil)
kdebug:db:match(/usr/local/texlive2007/texfm/fonts/tfm/public/lm/ec-lmr12.tfm,/usr/local/texlive2007/texfm/fonts) = 0
kdebug:search([ec-lmr12.ofm ec-lmr12.tfm]) =>
Relevant lines from texmf.cnf:
% A shortcut
TEXFONTS= $TEXMF/fonts
% Device-independent font metric files.
VFFONTS = .;$TEXFONTS/vf//
TFMFONTS = .;$TEXFONTS/tfm//
I don't have the variable OFMFONTS set.
%%%%%%%%%%%%%% %%%%%%%%%%%%%
I found that the reason was that the OFMFONTS variable is not set, even if I don't have any ofm file in my computer. Furthermore, setting it to ./ (in Windows I tried) does not solve the problem. I tryed with a dummy
OFMFONTS = $TFMFONTS
and it works.
Note that my first message some months ago was entitled "Keep looking for ofm files, why?"
--Javier A.