when i update my page i see this error and i tried to fix it but useless. I removed all plugins and checked but not fixed. Then i removed all themes and install other theme but still it is not fixed. Now i am confused how to fix it. Please guide me how to fix it and why this error is showing? Thanks
That may not be a valid error. But the troubleshooting link provided in a comment to your question is a good place to start. Error logs are great help.
You should also provide additional info (edit your question). When does this happen? All pages? Admin area only? Alternate Tuesdays?
Make sure that you install themes/plugins only from the WP repository. There have been instances of malware'd plugins/themes causing problems.