Test your theme before uploading to wordpress, all errors will be shown in an admin page.
1) Check Theme Errors:
http://wordpress.org/extend/plugins/theme-check/
2) Logs the usage of deprecated files, functions, and function arguments, and identifies where the deprecated functionality is being used.
http://wordpress.org/extend/plugins/log-deprecated-notices/
3) This plugin will allow you to check your entire site against the W3C Validator.
http://wordpress.org/extend/plugins/validated/
4) Debug theme, validates xhtml, Theme Check
. Also, use the minimized tag syntax for empty elements, e.g.
sorry, this theme breaked my post, as it contain some html markup . . .how can I put html in post?