submission error

While the user submits post from frontend,the post submits,but instead of diplaying success message it display like this:

The page cannot be found

The page you are looking for might have been removed, had its name changed, or is temporarily unavailable.
Please try the following:

Make sure that the Web site address displayed in the address bar of your browser is spelled and formatted correctly.
If you reached this page by clicking a link, contact the Web site administrator to alert them that the link is incorrectly formatted.
Click the Back button to try another link.
HTTP Error 404 – File or directory not found.
Internet Information Services (IIS)

Technical Information (for support personnel)

Go to Microsoft Product Support Services and perform a title search for the words HTTP and 404.
Open IIS Help, which is accessible in IIS Manager (inetmgr), and search for topics titled Web Site Setup, Common Administrative Tasks, and About Custom Error Messages.

its very urgent give me some suggestion

https://wordpress.org/plugins/wp-user-frontend/