Ssh – SCP transfer doesn’t work and SSH ls freezes

I am trying to copy some file via ssh with a SSH-RSA public key. I've already accepted the host key in my server and viceversa so the keys are synchronized. Now I try to connect via SSH to the host and I success, but it freezes if I invoque an "ls" in some folders. Also I try to do an scp request as follows:

scp -v username@host_ip:/folder/folder1/file.txt /home/user/Desktop

And I get this answer:

OpenSSH_5.3p1, OpenSSL 1.0.0-fips 29 Mar 2010
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to <ip_host> [<ip_host>] port 22.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: Host '<ip_host>' is known and matches the RSA host key.
debug1: ssh_rsa_verify: signature correct
debug1: Authentication succeeded (publickey).
debug1: channel 0: new [client-session]
debug1: Entering interactive session.
debug1: Sending environment.
debug1: Sending env LANG = fr_FR.UTF-8
debug1: Sending command: scp -v -f /folder/folder1/file.txt
Sending file modes: C0664 3352 file.txt
Sink: C0664 3352 file.txt
file.txt                                0%    0     0.0KB/s   --:-- ETA^
file.txt                                0%    0     0.0KB/s - stalled -^

I have searched and I have tried to change the MTU from 1500 to 1492 but nothing has changed. Does anyone have any clue of what could it happen? Thanks a lot.