can't connect to sftp server

[SamuelB-ACA]

I can't connect from server1 to server2. I only get the 'Resource temporarily unavailable' message. The sysadmin at server2 told me he could connect with the same command. I'm runnig out of ideas

lftp --version
LFTP | Version 4.9.2 |

uname -a
FreeBSD server1.com 11.2-PRERELEASE FreeBSD 11.2-PRERELEASE #0 r334634M: Tue Jun  5 11:22:03 UTC 2018     [email protected]:/build/kernel/objs/usr/src/sys/SOMETHING_11  amd64

command

lftp -d -c 'set sftp:connect-program "ssh -a -x -i /path/to/mykey"; connect sftp://user.name:[email protected];ls;'
`ls' at 0 [Resource temporarily unavailable]

while

ssh -vvv -a -x -i /path/to/mykey -s -l user.name:[email protected] sftp

...
debug1: Trying private key: /path/to/mykey
debug1: Enabling compression at level 6.
debug1: Authentication succeeded (publickey).
Authenticated to sftp.server2.com ([123.123.123.123]:22).
debug1: channel 0: new [client-session]
debug1: Entering interactive session.
debug1: pledge: network
debug1: Sending subsystem: sftp
...
debug3: send packet: type 80
debug3: receive packet: type 82
...
debug3: send packet: type 80
debug3: receive packet: type 82
...