how to fix this error

Assuming you’re talking about a plugin you yourself are writing… all plugins need to start with the right header.

If you’re talking about someone else’s plugin, ask them.

<?php
/*
Plugin Name:
Plugin URI:
Description:
Author:
Version:
Author URI:
/*

<and now my code....>

i altered the files and then uploaded&activated it once again but its saying me the same error[The plugin does not have a valid header.]

Share your code? here or at pastebin.

ive altered the plugins and the header information for the plugin [j-post-slider]and inserted the code like this in the php file
/*
Plugin Name:
Plugin URI:
Description:
Version:
Author:
Author URI:
*/and the information to filled in it after altering it im encountered by the same error

Can you share your WHOLE code?

Wrap it in code tags (see the code button above the text entry area? Use that ?? ) but basically the fast answer is you put in bad header info. No one can help you fix it without seeing what you really have.

this is the i have entered the information before that it doesn’t have this header `<?
/*
Plugin Name: J Post Slider
Plugin URI: https://www.prodeveloper.org/j-post-slider-wordpress-plugin-jquery-post-animation-show.html
Description: Show your post in fancy jQuery box, rotating images, with show-up text box with post description. Mousover stop the animation, and user can click on post link anytime ;)I used Boban Kari??ik s3Slider jQuery scipt. Thanks Boban for nice jQuery script. I can’t show you how much cool is this plugin, you just need to try it.
Version: 1.3.1
Author: Ivan Djurdjevac
Author URI: https://www.prodeveloper.org
*/
include_once(“./../../../wp-blog-header.php”);
include_once(“jslider.php”);
echo js_media_button_ajax($_GET[‘postid’]);
?>`

Try taking out the ?? in your description.

<?
/*
Plugin Name: J Post Slider
Plugin URI: https://www.prodeveloper.org/j-post-slider-wordpress-plugin-jquery-post-animation-show.html
Description: Show your post in fancy jQuery box, rotating images, with show-up text box with post description. Mousover stop the animation, and user can click on post link anytime I used Boban Kari??ik s3Slider jQuery scipt. Thanks Boban for nice jQuery script. I can't show you how much cool is this plugin, you just need to try it.
Version: 1.3.1
Author: Ivan Djurdjevac
Author URI: https://www.prodeveloper.org
*/

include_once("./../../../wp-blog-header.php");
include_once("jslider.php");
echo js_media_button_ajax($_GET['postid']);

?>

hai sorry for my delayed reply i did the changes that are listed in the last topic but after that also its saying me the same msg [The plugin does not have a valid header.] what me the perfect solution for this

Y’know, it helps if you put in the error message:

Warning: include_once(./../../../wp-blog-header.php) [function.include-once]: failed to open stream: No such file or directory in /public_html/blog/wp-content/plugins/jslider.php on line 11

First, in WP 2.5 and up, the file location should be ../../wp-blog-header.php

Second, the wp-blog-header.php file is already called somewhere by the admin header section with the require_once() PHP function.

Solution:
Remove that line from your plugin, and party on, Garth.