This is a PDFTeX error: PDFTeX is running in PDF output
mode, and it has encountered a
\special command. PDFTeX is
able to generate its own output, and in this mode of operation has no
need of \special commands (which allow the user to pass
information to the driver being used to generate output).
Why does this happen? LaTeX users, nowadays, hardly ever use
\special commands on their own - they employ packages to do the
job for them. Some packages will generate \special commands
however they are invoked: pstricks is an example (it's very
raison d'être is to emit PostScript code in a sequence of \special
commands). Pstricks may be dealt with by other means (the
pdftricks package offers a usable technique).
More amenable to correction, but more confusing, are packages (such as
color, graphics and hyperref) that
specify a "driver". These packages have plug-in modules that
determine what \special (or other commands) are needed to generate
any given effect: the pdftex driver for such packages knows not to
generate \special commands. In most circumstances, you can let
the system itself choose which driver you need; in this case
everything will act properly when you switch to using PDFLaTeX. If
you've been using dvips (and specifying the dvips driver)
or dvipdfm (for which you have to specify the driver), and
decide to try PDFLaTeX, you must remove the dvips or
dvipdfm driver specification from the package options, and let the
system recognise which driver is needed.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=nonpdfsp