Passbook not recognising a barcode. What can I do?

I'm trying to scan a barcode for the cinema on Passbook but it doesn't recognise it. It says 'no pass available for this code - please look for the "add to passbook" sign' which is right underneath the barcode! I'm pretty sure this isn't the first time Passbook hasn't recognised a barcode. Could it be something to od with my computer screen? What can I do?