Error 44 is a FASP error that refers to connectivity problems between the remote and the local machine of a transfer. When a transfer is attempted, a TCP connection must be made between the two machines to establish SSH authentication, and then a connection using UDP ports must be made to conduct the actual FASP transfer.
A UDP session can fail to initiate for a number of reasons, but a common one is the TCP connection being unable to be made in the first place, perhaps because of internet connectivity issues or problems with SSH. If the TCP connection cannot start, neither can the UDP session.
Examples of this error
When attempting to transfer with a remote server that has problems with SSH or general internet connectivity, you see the following error in the GUI or on the command line:
Error: Failed to open TCP connection for SSH
On the GUI, you may also see an error window like the one below when trying to connect to a remote host:
aspera-scp-transfer.log file records helpful information for each attempted transfer, labelled by the date and time attempted. For a reference of the location of this log file on your system, please see this article (Where are the Client or Server logs located?). A sample of what would be logged for a failed transfer with error code 44 is the following:
2015-04-30 11:13:34 [3ef3-0xa116d1d4] ERR Failed to open TCP connection for SSH
2015-04-30 11:13:34 [3ef3-0xb0103000] LOG FASP Session Start uuid=ab5ca8ca-da6e-4957-b74c-cad67dc77b88 op=send
status=failed errcode=44 errstr="UDP session initiation fatal error"
Ensure that the remote server has proper internet connectivity, and that SSH is working as expected.
You should also verify that the SSH port is open and not being blocked by a firewall. The default TCP port for SSH is 22, but you may be using a different one for your Aspera server, such as 33001.
For Windows, you can check and configure your firewall by following the instructions at the following article: Configuring Windows Firewall to enable Aspera FASP transfers.
On many Linux systems the default firewall can be configured with
iptables. You will have to allow all incoming and outgoing traffic on UDP port 33001 (or whatever your Aspera UDP port is), which you can do with the following commands:
# iptables -I INPUT -p tcp --dport 33001 -j ACCEPT
# iptables -I OUTPUT -p tcp --dport 33001 -j ACCEPT