Users can't login by SFTP, root can (SSH works fine)

[Boris Spremo <bspremo@xxxxxx>]

Hello,

after a long time of normal operation, users can't login using SFTP to 
one of my machines. Root SFTP login works fine. All SSH logins work fine 
as well. No system related configuration files have been changed in a 
long while.

Here's the OpenSSH client output:

[...]
debug1: Authentication succeeded (password).
debug1: channel 0: new [client-session]
debug1: Entering interactive session.
debug1: Sending environment.
debug1: Sending env LANG = en_US
debug1: Sending subsystem: sftp
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: channel 0: free: client-session, nchannels 1
debug1: fd 0 clearing O_NONBLOCK
debug1: Transferred: stdin 0, stdout 0, stderr 0 bytes in 0.0 seconds
debug1: Bytes per second: stdin 0.0, stdout 0.0, stderr 0.0
debug1: Exit status 1
Connection closed


SSHD debug output shows nothing out of the ordinary for both root and 
ordinary user (ceadmin):

subsystem request for sftp
debug1: subsystem: exec() /usr/sbin/sftp-server
debug1: audit run command euid 0 user root command '/usr/sbin/sftp-server'
debug1: Received SIGCHLD.
debug1: session_by_pid: pid 508114
debug1: session_exit_message: session 0 channel 0 pid 508114
debug1: session_exit_message: release channel 0
debug1: session_by_channel: session 0 channel 0
debug1: session_close_by_channel: channel 0 child 0
debug1: session_close: session 0 pid 0
debug1: channel 0: free: server-session, nchannels 1
Connection closed by *.*.*.*
debug1: do_cleanup
Closing connection to *.*.*.*
debug1: audit event euid 0 user root event 11 (SSH_connclose)
debug1: Return Val-1 for auditproc:0

subsystem request for sftp
debug1: subsystem: exec() /usr/sbin/sftp-server
debug1: audit run command euid 0 user ceadmin command 
'/usr/sbin/sftp-server'
debug1: Received SIGCHLD.
debug1: session_by_pid: pid 508104
debug1: session_exit_message: session 0 channel 0 pid 508104
debug1: session_exit_message: release channel 0
debug1: session_by_channel: session 0 channel 0
debug1: session_close_by_channel: channel 0 child 0
debug1: session_close: session 0 pid 0
debug1: channel 0: free: server-session, nchannels 1
Connection closed by *.*.*.*
debug1: do_cleanup
Closing connection to *.*.*.*
debug1: audit event euid 0 user ceadmin event 11 (SSH_connclose)
debug1: Return Val-1 for auditproc:0

Syslog shows nothing out of the ordinary, as well.

OS is AIX 5.3-08
Version is OpenSSH_5.0p1, OpenSSL 0.9.8h 28 May 2008 (shipped with OS)
Uptime is 460 days.
OpenSSH, AnyClient and FileZilla clients have been used from different 
machines.

I can post full sshd debug output for both cases if needed.

Thanks in advance.

Kindest regards,
--
Boris Spremo