how can I fix this problem? I'm not engineer so please let me know the way to fix without coding.

[Sunny Yi]

I'm editing many pages, but when I pressed publish button, system poped up, and then could not publish. after logout and log in again, and then same situation happened. T.T

popup said,

"Can't connect to the server

your session has expired. You'll need to log in again or switch to another account to keep working.<div><a href="/login?application=confluence">Log in or switch to another account</a></div>

please let me know the way to fix without coding.

[Nic Brough -Adaptavist-]

There is nothing to fix with coding here.

If you open up a web site that has account based access to it, then a standard practice is for the server to close down your session after it has not been active for a while.  It's a security measure more than anything - you should close inactive sessions because you don't know who might pick them up and do bad things with them.  Timeouts vary between sites, you'll find banks have very short ones, less sensitive systems have longer ones.

The simple thing here is that your session expired, so it asked you to start a new one.  It couldn't keep the entered information because that was in the session and that had gone away.