Try:
connection.setRequestProperty("Range", "bytes=" + fcheck.length() + "-");
Lowercase the range specifier per the spec. Also, if your partial file was 500 bytes, that means your byte range that you have is 0-499, and you want 500+.
Try:
connection.setRequestProperty("Range", "bytes=" + fcheck.length() + "-");
Lowercase the range specifier per the spec. Also, if your partial file was 500 bytes, that means your byte range that you have is 0-499, and you want 500+.