Cannot insert media, error message

Fatal error: Call to undefined function get_post_mime_types() in /home/xxxxxx/public_html/noonecaresaboutwhatyoudo.com/wp-admin/includes/media.php on line 1157

that’s what i see when i try to insert the media into my posts. i know they’re still uploading because i can see them in media>library, i just can’t use them.

i use the theme videographex, just before this happened my friend that does some simple coding for me installed the postmash plugin, but he doesn’t think he edited anything that would’ve caused this.

i really appreciate any help. thanks.

-justin