There is nothing that can directly be done about this error: you can’t extend the number of available! No room for a new \dimen.
dimenregisters without extending TeX itself. Omega and e-TeX both do this. It’s actually quite practical (with most modern distributions) to use e-TeX’s extended register set: use package etex (which comes with e-TeX distributions) and the allocation mechanism is altered to cope with the larger register set: PicTeX will now load. If you’re in some situation where you can’t use e-TeX, you need to change PicTeX; unfortunately PicTeX’s author is no longer active in the TeX world, so one must resort to patching. There are two solutions available. The ConTeXt module m-pictex.tex (for Plain TeX and variants) or the corresponding LaTeX m-pictex package provide an ingenious solution to the problem based on hacking the code of
newdimenitself. Alternatively, Andreas Schrell’s pictexwd and related packages replace PicTeX with a version that uses 33 fewer
dimenregisters; so use pictexwd in place of pictex (either as a LaTeX package, or as a file to read into Plain TeX). And how does one use PicTeX anyway, given that the manual is so hard to come by? Fortunately for us all, the MathsPic system may be used to translate a somewhat different language into PicTeX commands; and the MathsPic manual is free (and part of the distribution). MathsPic is available either as a Basic program for DOS, or as a Perl program for other systems (including Windows, nowadays).
This answer last edited: 2014-01-22
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