Problem with automatic start

I had an automatic start installed in my 2001 Cavalier over 3 years ago. I had also purchased the extended reach antenna for the auto start so I could start it from across a parking lot. It worked fine, except now it's not working. It will only work if I'm standing right in front of the car. So I know the automatic start is still working, but what do I have to do to get it to work from a distance again?

Please help.

Thank you.
Susan

Try a new battery in the remote.

I did try a new battery in the remote. Actually, it was the first thing that I tried. Could it be something with the extended reach antenna? As I said, it does work if I'm standing right in front of it.