Upoad file error in Apache Guacamole: File transfer is either not supported or not enabled

Question

I am using Apache Guacamole as my ssh web proxy to connect to a remote computer, but when I use SFTP to upload files from my local computer, it has the probability of upload failing. The failing message is "File transfer is either not supported or not enabled. Please contact your system administrator, or check your system logs." After then, I retry it, it would succeed. I want to know the root cause of the upload failing, I have confirmed the Tomcat log(catalina.out) and guacd process log(/var/log/messages), but I did not find any clues. Is there anyone who encountered this issue or has any idea about this?