Strict Standards Errors all Of A Sudden

Hi Guys, i’ve been using wordpress now for over a year and have never had any issues before. All of a sudden one of my websites does not display correctly due to several strict standard errors, the website does not view correctly and there are the following errors on the dashboard. The website has been working fine with the latest version of wordpress 3.7.1 and i have not upgraded my php version on my server, all my other websites seem fine, just this one, nothing has been changed to produce the errors, they just occurred suddenly, the errors are:

Strict Standards: call_user_func_array() expects parameter 1 to be a valid callback, non-static method Thememakers_Entity_Portfolio::register() should not be called statically in /homepages/5/d439351399/htdocs/westmidssols/wp-includes/plugin.php on line 429

Strict Standards: call_user_func_array() expects parameter 1 to be a valid callback, non-static method Thememakers_Entity_Testimonials::register() should not be called statically in /homepages/5/d439351399/htdocs/westmidssols/wp-includes/plugin.php on line 429

Strict Standards: call_user_func_array() expects parameter 1 to be a valid callback, non-static method Thememakers_Entity_Gallery::register() should not be called statically in /homepages/5/d439351399/htdocs/westmidssols/wp-includes/plugin.php on line 429

Strict Standards: call_user_func_array() expects parameter 1 to be a valid callback, non-static method GoogleSitemapGeneratorLoader::Enable() should not be called statically in /homepages/5/d439351399/htdocs/westmidssols/wp-includes/plugin.php on line 429

Strict Standards: call_user_func_array() expects parameter 1 to be a valid callback, non-static method GoogleSitemapGeneratorLoader::RegisterAdminPage() should not be called statically in /homepages/5/d439351399/htdocs/westmidssols/wp-includes/plugin.php on line 429

Strict Standards: Non-static method GoogleSitemapGeneratorLoader::GetBaseName() should not be called statically in /homepages/5/d439351399/htdocs/westmidssols/wp-content/plugins/google-sitemap-generator/sitemap.php on line 114

Strict Standards: call_user_func_array() expects parameter 1 to be a valid callback, non-static method GoogleSitemapGeneratorLoader::CallHtmlShowHelpList() should not be called statically in /homepages/5/d439351399/htdocs/westmidssols/wp-includes/plugin.php on line 199

Strict Standards: Non-static method GoogleSitemapGeneratorLoader::GetBaseName() should not be called statically in /homepages/5/d439351399/htdocs/westmidssols/wp-content/plugins/google-sitemap-generator/sitemap.php on line 199

Someone said on this forum it happened to them and about 15 minutes later it corrected itself without doing anything, thanks in advance guys… 🙂