Thanks for the response!,
I finally got the answer... and it is that i didn't realize that while the exportwebmap job executes in the server side, uses the Rest services links sent from the client. This is a problem in my case because, from inside my company, we can't access the public url of my web page due some problems with the configuration of our ISP. So when the job recieved the links of our services to execute the printtask, this task used these external links, which weren't available, that's why the "Unable to connect to map server" message appeared. To fix this I had to add a line to my server hosts file:
server private IP url public application url
# 127.0.0.1 localhost
and so now my server can resolve the public url, redirecting it to my local server IP, and the proccess completes.
Thanks again for the help
Rinat S.