The problem is solved: With the help of the Vegan library maintainer the error was found immediately. It was a misinterpretation/overlooking of the provided documentation.
The problem lies here: > > meta <- metaMDS(distab.dist, distance="bray", k, trymax=50) The provided primary data matrix - distab.dist - was in my case a distance matrix, not a original data set matrix as demanded in the documentation. As Jari Oksanen told me, several other users seem to have been trapped by the same pragmatic error also, which are reported in his newer versions of the Vegan library only. At least version 1.6-10 ran smoothly without reporting an error, thus leaving the user with the faulty notion of a correctly running program. It seems that the pragmatic error of not only me stemmed from the fact that the frequently used methods cmdscale and isoMDS from the original R distribution scope require indeed *distance matrices* as their first input value. So, switching from them to the Vegan metaMDS, makes one easily overlook the important change in required data structure. The error condition that the newer versions of Vegan now returns helps to detect this faulty data provision. Kind regards and many thanks to the list and the maintainer, Peter ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.