Portfolio Gallery error (pic included)

Hi
I encountered an error(below) when i wanted to add photos to my slider in the portfolio page.

“<# _.each( attachments, function( attachment ) { #> <# if ( attachment.sizes.hasOwnProperty( ‘thumbnail’ ) ) { #>”

http://5.9.123.24:2082/cpsess8967076766/viewer/home%2fstpcompa%2fpublic_html%2fHelp/error.jpg

the portfolio page has a slider with thumbnail navigation underneath. the photos which are correct in ratio are from theme demo, and those incorrect are the ones i tried to add.

http://5.9.123.24:2082/cpsess8967076766/viewer/home%2fstpcompa%2fpublic_html%2fHelp/Error2.jpg

i’m desperately in need of help to fix this problem.