Here is my story.

Taking the advice you guys gave me, I emailed again 'Supervisor A' that I had lost contact with before and eventually got a reply from him. However, I wanted to cry when I read his reply. He is not so positive about my project, saying that the approach and the data I chose are a problem and my project is not doable. So he asked me to revise my project. Now the problem is that I will not have enough time to revise it due to my heavy workload in my full time job. More importantly, the deadline for PhD applications is early Dec, which means that I only have a few weeks to re-read a lot of books and articles and then revise the project. How can I finish it on time?

At the same time, I got another reply from 'Supervisor B' of another university. In his email, he seems positive about my project, saying that it is doable even though he asked me to revise my project a bit. He also asked me to meet him to further discuss the project.

I am feeling confused now. Both the supervisors are Professors of their own field of study. How come did I receive two different responses to the same project? When I meet my potential supervisor, should I mention the problem that Supervisor A pointed out?

Hmm...

It is possible that 'Supervisor A' was not being entirely honest with you. Perhaps they had an ulterior motive to trying to persuade you not to apply for a PhD with them? Perhaps it doesn't interest them. That doesn't mean that it's not doable or could even make a seminal contribution to mankind...

As to whether or not to mention 'Supervisor A' to 'Supervisor B' I'm not too sure. But by the sounds of things 'Supervisor B' is supportive of your ideas and so perhaps he is a keeper!