Hi,
thanks for the suggestions. None of this worked, but I found the solution.
TagAnt had problems only with two files that were originally encoded in ASCII; after converting them to UTF-8 the problem was still there.
I browsed through the files in notepad++, found one "sub" (substitution character, right?) in each file, deleted the "sub" and then TagAnt worked.
Sorry to have bothered you and thanks for your help and time, and four your amazing tools, of course! Could have said that earlier ;)
Best,
Alex