I am not able to express interest in some of the profiles, why?
You can't send Interest to every member, it depends on the other member's partner preference. So based on the partner preference he/she has provided you will be able to Express Interest. But, we are not matching each and every minor information. Even if you think that they can consider your request then you have to go for Paid membership where you will be able to send the message to request them for consideration.