Getting "java.nio.charset.UnmappableCharacterException: Input length = 1"

I am getting UnmappableCharacterException on the collect() method call (or on the toList() call):

    private static void handleTransaction(Path a_filePath, String a_sTrasactionName, String a_sTransactionFilePath) {

    // read file into stream, try-with-resources
    try (Stream<String> stream = Files.lines(Paths.get(a_filePath.toString()), Charset.defaultCharset())) {

        List<String> list =
            stream.filter(line -> (line.indexOf(a_sTrasactionName) > 0))
            .collect(Collectors.toList());

        list.forEach(line -> {

            System.out.println(line);

            try (BufferedWriter writer = Files.newBufferedWriter(Paths.get(_FILES_PATH + a_sTransactionFilePath),Charset.defaultCharset(), StandardOpenOption.APPEND)) {
                writer.write(line + "\n");
            } catch (IOException e) {
                e.printStackTrace();
            }
        });
    } catch (IOException e1) {

        e1.printStackTrace();
    }

It worked for me once, but never since then.

The files I read are csv files which were created on solaris. I run the jar on Windows 2012 server

Can you advise please?

Thank you.