what version is SQL Developer, and your databases?
check your database alert log's for ORA-600's or other bad things around your connection
if you just copy a few objects (I don't know what you're actually copying...), does it work? or does it break even for one table with one row?
Hello and thank you for your reply.
SQL Dev: 4.2
I will go through the logfiles and look for some bad things.
The Connection breaks even with only one object to copy.