The server is proFTPd.
When using FTP everything works just fine.
When using SFTP uploading a file produces the following log:
DEBUG [SshPublicKeyFile] 1 Aug 2012 13:07:03.299 : Parsing public key file
DEBUG [SshPublicKeyFile] 1 Aug 2012 13:07:03.308 : Public key is not in the default format, attempting parse with other supported formats
DEBUG [SshPublicKeyFile] 1 Aug 2012 13:07:03.309 : Attempting SECSH-PublicKey-Base64Encoded
DEBUG [SshPublicKeyFile] 1 Aug 2012 13:07:03.309 : Attempting OpenSSH-PublicKey
DEBUG [AbstractKnownHostsKeyVerification] 1 Aug 2012 13:07:03.335 : Allowing poursftp.ftptoday.com with fingerprint 2048: 1c 51 f5 94 a2 b1 e f4 d0 54 bf 1b d0 3b 30 c1
WARN [AbstractKnownHostsKeyVerification] 1 Aug 2012 13:07:03.337 : Cannot write to known_hosts file as none supplied
INFO [SCPClient] 1 Aug 2012 13:07:03.352 : SCPClient settings validated.
DEBUG [SCPClient] 1 Aug 2012 13:07:03.353 : Connecting to poursftp.ftptoday.com:22
DEBUG [StreamSocketFactory] 1 Aug 2012 13:07:03.364 : Connecting to poursftp.ftptoday.com:22 via standard socket
INFO [TransportProtocolCommon] 1 Aug 2012 13:07:03.465 : Timeout=60000
DEBUG [SshKeyPairFactory] 1 Aug 2012 13:07:03.465 : Setting preferred keypair = ssh-rsa
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.466 : Starting transport protocol
INFO [TransportProtocolCommon] 1 Aug 2012 13:07:03.471 : Wait for state update timeout=60000
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.471 : Registering transport protocol messages with inputstream
INFO [cryptix] 1 Aug 2012 13:07:03.490 : GLOBAL_TRACE=false
INFO [cryptix] 1 Aug 2012 13:07:03.490 : GLOBAL_DEBUG=false
INFO [cryptix] 1 Aug 2012 13:07:03.490 : GLOBAL_DEBUG_SLOW=false
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.491 : Negotiating protocol version
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.491 : Local identification: SSH-2.0-edtFTPjPRO-4.2.0
'
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.511 : EOL is guessed at CR+LF
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.511 : Remote identification: 'SSH-2.0-mod_sftp/0.9.7'
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.511 : Protocol negotiation complete
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.512 : Name=SSH_MSG_KEX_INIT,MessageId=20
Supported Kex diffie-hellman-group1-sha1,diffie-hellman-group-exchange-sha1
Supported Public Keys ssh-rsa,ssh-dss
Supported Encryption Client->Server aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc,aes128-ctr,aes192-ctr,aes256-ctr,blowfish-cbc,arcfour
Supported Encryption Server->Client aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc,aes128-ctr,aes192-ctr,aes256-ctr,blowfish-cbc,arcfour
Supported Mac Client->Server hmac-sha1,hmac-sha1-96,hmac-md5,hmac-md5-96
Supported Mac Server->Client hmac-sha1,hmac-sha1-96,hmac-md5,hmac-md5-96
Supported Compression Client->Server none,zlib,zlib@openssh.com
Supported Compression Server->Client none,zlib,zlib@openssh.com
Supported Languages Client->Server
Supported Languages Server->Client
First Kex Packet Follows [FALSE]
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.515 : Sending SSH_MSG_KEX_INIT
INFO [TransportProtocolCommon] 1 Aug 2012 13:07:03.516 : Wait for state update timeout=60000
DEBUG [SshMsgKexInit] 1 Aug 2012 13:07:03.517 : Packetlength=676, Paddinglength=5
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.517 : Received registered message: SSH_MSG_KEX_INIT
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.518 : Received Name=SSH_MSG_KEX_INIT,MessageId=20
Supported Kex diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1,rsa1024-sha1
Supported Public Keys ssh-rsa,ssh-dss
Supported Encryption Client->Server aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,blowfish-ctr,blowfish-cbc,cast128-cbc,arcfour256,arcfour128,3des-ctr,3des-cbc
Supported Encryption Server->Client aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,blowfish-ctr,blowfish-cbc,cast128-cbc,arcfour256,arcfour128,3des-ctr,3des-cbc
Supported Mac Client->Server hmac-sha1,hmac-sha1-96,hmac-md5,hmac-md5-96,hmac-ripemd160
Supported Mac Server->Client hmac-sha1,hmac-sha1-96,hmac-md5,hmac-md5-96,hmac-ripemd160
Supported Compression Client->Server zlib@openssh.com,zlib,none
Supported Compression Server->Client zlib@openssh.com,zlib,none
Supported Languages Client->Server
Supported Languages Server->Client
First Kex Packet Follows [FALSE]
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.521 : Starting key exchange
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.521 : Determine Algorithm
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.522 : Client Algorithms: [diffie-hellman-group1-sha1, diffie-hellman-group-exchange-sha1]
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.522 : Server Algorithms: [diffie-hellman-group-exchange-sha256, diffie-hellman-group-exchange-sha1, diffie-hellman-group14-sha1, diffie-hellman-group1-sha1, rsa1024-sha1]
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.523 : Returning diffie-hellman-group1-sha1
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.524 : Key exchange algorithm: diffie-hellman-group1-sha1
INFO [DhGroup1Sha1] 1 Aug 2012 13:07:03.524 : Starting client side key exchange.
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.536 : Sending SSH_MSG_KEXDH_INIT
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.600 : Received unregistered message: SSH_MSG_KEXDH_REPLY
DEBUG [DhGroup1Sha1] 1 Aug 2012 13:07:03.606 : calculateExchangeHash()
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.610 : Verifying host poursftp.ftptoday.com,74.126.94.98
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.611 : Preferred algorithm ssh-rsa
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.611 : Selected algorithm ssh-rsa
DEBUG [SshRsaPublicKey] 1 Aug 2012 13:07:03.611 : Signature length=271
DEBUG [SshRsaPublicKey] 1 Aug 2012 13:07:03.615 : Verifying signature (com.enterprisedt.cryptix.provider.rsa.SHA1_RSA_PKCS1Signature)
DEBUG [AbstractKnownHostsKeyVerification] 1 Aug 2012 13:07:03.618 : verifyHost - found matching entry for host 'poursftp.ftptoday.com,74.126.94.98'
DEBUG [AbstractKnownHostsKeyVerification] 1 Aug 2012 13:07:03.619 : verifyHost - found matching algorithm 'ssh-rsa'
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.620 : Sending SSH_MSG_NEWKEYS
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.620 : Received registered message: SSH_MSG_NEWKEYS
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.621 : Completing key exchange
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.621 : Making keys from key exchange output
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.622 : Creating algorithm objects
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.622 : setupNewKeys
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.622 : Determine Algorithm
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.623 : Client Algorithms: [aes128-cbc, 3des-cbc, aes192-cbc, aes256-cbc, aes128-ctr, aes192-ctr, aes256-ctr, blowfish-cbc, arcfour]
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.623 : Server Algorithms: [aes256-ctr, aes192-ctr, aes128-ctr, aes256-cbc, aes192-cbc, aes128-cbc, blowfish-ctr, blowfish-cbc, cast128-cbc, arcfour256, arcfour128, 3des-ctr, 3des-cbc]
DEBUG [TransportProtocolCommon] 1 Aug 2012 13:07:03.624 : Returning aes128-cbc
DEBUG [SshCipherF
