this means your file is being used by another user(locked). Make sure if you are logged in twice into the same machine with the same user, you close one of the sessions.

For example, we had a customer who was logged in twice with root from from different computers using his SSH. He was at work logged in, and he remembered that he also was logged in when he left home from work. So that meant he was logged in as root from home using a SSH connection, and when he got to work, he also logged in as root . When he tried to use the same file (httpd.conf) from work, he couldn't because his session at home was also using the file httpd.conf.

He needed to have his computer the home release the httpd.conf file. But since he was at work, he couldn't do that. The only suggestion we could provide was to reboot the server remotely from work. After he did that, the server rebooted and all the connections (users loggedin) were dropped. When the server rebooted, he logged in with SSH and was able to edit his httpd.conf file.

so basically, if you are getting this error, its because the file is being used by another user. If you are stuck with this issue, do a reboot and that should clear your problem.

above method of rebooting the machine seems to be difficult when we don't have access to do so.
is there any method or configuration that can solve this problem which provides multiple login from the same user.