Thanks for the answer. I already read it in another thread two minutes after. :) Whereas I can't second that interpretation for it's definitely a syntactical adverb. It is dependant on the verb. But I guess languages are always a bit querky, but it's enough for me to know, that "sole" is correct, too.
It's a really good question. For me
"Mi ne ŝatas vojaĝi sola" which should be equivalent to "Mi sola ne ŝatas vojaĝi" has to be translated with: "I'm alone who don't like to travel"
While the correct translation for "I don't like traveling alone" should be "Mi ne ŝatas vojaĝi sole"