Getting the post thumbnail URL

Fatal error: Uncaught Error: Call to a member function id() on array in /home/appcropolis_clean/sanraul.com/public/wp-content/plugins/crayon-syntax-highlighter/crayon_formatter.class.php:36 Stack trace: #0 /home/appcropolis_clean/sanraul.com/public/wp-content/plugins/crayon-syntax-highlighter/crayon_formatter.class.php(538): CrayonFormatter::format_code('', Array, Object(CrayonHighlighter)) #1 [internal function]: CrayonFormatter::delim_to_internal(Array) #2 /home/appcropolis_clean/sanraul.com/public/wp-content/plugins/crayon-syntax-highlighter/crayon_formatter.class.php(516): preg_replace_callback('#()#msi', 'CrayonFormatter...', 'include ('wp-bl...') #3 /home/appcropolis_clean/sanraul.com/public/wp-content/plugins/crayon-syntax-highlighter/crayon_highlighter.class.php(166): CrayonFormatter::format_mixed_code('include ('wp-bl...', Object(CrayonLang), Object(CrayonHighlighter)) #4 /home/appcropolis_clean/sanraul.com/public/wp-content/plugins/crayon-syntax-highlighter/crayon_highlighter.class.php(186): CrayonHighlighter->p in /home/appcropolis_clean/sanraul.com/public/wp-content/plugins/crayon-syntax-highlighter/crayon_formatter.class.php on line 36