Hello,
Yes, that error message is not the same thing as saying there are no
available results. It may be that the keyword variation backend server
used by the API and the web interface has an upper bound on the number
of words it'll except in a given seed keyword. Try paring down the
number of words in your request some, and getting rid of the duplicate
words.
Also note that in general, if you pass something that long into the
keyword variations service you'll get much fewer results back than if
you pass in a single word or a short phrase.
Cheers,
-Jeff Posnick, AdWords API Team