[pracjourn-forum] A weird error

[Karl Berry]

    ! Undefined control sequence.
    <recently read> \c at lor@to at ps

When I run your document with latex, it works fine for me.
When I run your document with pdflatex, I get the error above.

Here, the story is that pstricks does not work "straight" with pdflatex,
for various technical reasons.  There are several ways to work around
this, as elucidated in:
  http://tug.org/TUGboat/Articles/tb22-4/tb72voss4pdf.pdf
The simplest is just to run "latex", and then either dvipdfm or
dvips+ps2pdf.

I cannot quite imagine any rational way that you could glean information
from the error message or log file to determine this.  The only viable
answer I can think of is for pstricks to detect that it is running under
pdflatex (which is doable) and give a meaningful error.  I will write
Herbert Voss about it.

    with undeifined control sequences for things I never typed....

Indeed.  The general answer is that the log file lists every file input
by TeX (unfortunately not in a very convenient form).  If you search
those files for the string in question ("c at lor@to at ps" -- best to leave
off the backslash when searching) usually [though not always] you will
find it, which will at least tell you the package involved.  In this
case, "c at lor" is a clue that color might be involved, although that
doesn't say much.

Unfortunately I don't know of a tool to make this kind of searching
convenient.  I've wanted it myself, more than once.  Surely there's
something out there ...

Cheers,
k