TW-receiver set up, works fine but often comes up with Error While Saving issue

[Rayme]

I installed plugin_sendwheel_tw-receiver.json to my tiddlywiki successful and put tw-receiver-server.php in same folder with index.html, setup password and first works fine. But as long I use, it starts to come up with an error which can't save to server anymore.
The error message is

---

Error while saving:

Error:
Server Error: Authentication Failure

I have set chmod 777 to both index.html and tw-receiver-server.php, but error remains.
I use a vhost server with WordPress works perfectly.