When accessing a synchronization or analyzing the log files, you see an error which contains "411 Length required".
The details in the log should look like this:
<html> <head><title>411 Length Required</title></head> <body bgcolor="white"> <center><h1>411 Length Required</h1></center> <hr><center>nginx</center> </body> </html>
This typically happens on when you use a nginx server which does not support the chunked transfer encoding.
You should enable chunked transfer encoding for your nginx server or switch to another server which supports this - so far we haven't heard of any problems with apache servers.
There are two ways to enable chunked transfer encoding for your nginx.
Option 1: Update your nginx server
Update your nginx server to a current version. nginx added support for chunked transfer encoding with version 1.3.9 back in 2012. This is also recommended since there have been several security bugfix releases.
Option 2: Install an additional nginx module
Use the chunkin-nginx-module nginx versions prior to 1.3.9. See this documentation for more details.