Dreamweaver Quits When Put or Get

My site was set up on my Mac with OS 10.3.9. That one works fine when I upload
or download. I am switching to a new computer with 10.5.4. I copied all the
site files and set up the FTP on the new computer to upload to the server. I
copied all of the settings exactly (I've checked it several times). I tested
the connection and DW found the server. I chose a file to upload and clicked on
the "put files" button. I got a very quick "connected to server" message, then
DW quit and did not upload the files. It also does this when I click on the
"get files" button or "connects to remote host" button. My root folder is
Macintosh HD:Library:WebServer:sitefolder: . I don't have a test server set up.
I don't understand what's making it quit. My network speed and memory on my
computer are fine too.