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@Nikolay: I tried it with and without commenting out pst-all, didn't change a thing for the dvi. .ps-fils (and as you demonstrate pdf-files) work.
But thanks for being nice :) and helping.

@Stefan: Thanks for the advice. In particular for clearifing that I cannot really "directly" complile to ps ...

I want to use the sseq package. Not that it finally works the only remaining problem is that, when I create a DVI file it looks weird (see attachment). If I directly compile to PS everything works just fine.

When I compiled and viewed a slightly bigger file YAP created the following error message ...