Three times in the last two months I encountered a spate of 550 access denied errors when trying to transfer files to my website with FileZilla.
I contacted my web host, XO Communications (Concentric), and each time they claimed there was nothing wrong with their ftp server configuration.
The problem generally disappeared after a few hours, and I chalked it up to a process on the XO side having a directory locked during backup, or some other similar event.
Earlier this week it happened again. I cursed XO, complained to support and posted nasty things on social media, and waited for the problem to resolve itself. When it didn't, I became desperate and started checking everything.
A Google search for ftp 550 errors returned a number of hits containing references to Comcast, my broadband internet provider, blocking various ports for various reasons. One reason was out-of-date firmware.
Like a good Comcast customer, I didn't bother to call support... I just unplugged the router and hit reset on the cable modem.
It took a good five minutes for the modem to come back up, indicating a configuration change or firmware update was being performed. Once the reboot was completed, I plugged the router back in, waited for the computer to reconnect to the net, and the fired up the ftp client:
Command: STOR qcount.txt
Response: 150 Opening ASCII mode data connection for qcount.txt.
Response: 226 Transfer complete.
Status: File transfer successful, transferred 8 bytes in 1 second
Relieved, I regenerated my website pages and started formulating nasty things to say about Comcast. I clicked on the directory to have Filezilla send the files, and:
Response: 550 Access is denied.
Arrrgh!
What could have changed in the ten minutes between connect attempts?
I glanced at the Network and Sharing Center display I had opened after rebooting the modem to make certain all the machines on the home network were up. They were- along with a VPN connection to my office in Chicago, a connection I rarely use but had activated to connect via remote desktop to my workstation there.
I disconnected from the VPN and tried again:
Command: STOR qcount.txt
Response: 150 Opening ASCII mode data connection for qcount.txt.
Response: 226 Transfer complete.
Status: File transfer successful, transferred 8 bytes in 1 second
I restarted the VPN connection, and:
Response: 550 Access is denied.
Error: Critical file transfer error
I stopped the connection again. FileZilla now reported:
Error: Disconnected from server: ECONNABORTED - Connection aborted
Error: Disconnected from server: ECONNABORTED - Connection aborted
I resent the file:
Command: STOR qcount.txt
Response: 150 Opening ASCII mode data connection for qcount.txt.
Response: 226 Transfer complete.
Status: File transfer successful, transferred 8 bytes in 1 second
So, the problem wasn't XO's ftp server, or Comcast blocking ports. The active VPN connection resulted in a network configuration change that prevented FileZilla from opening a port to write data to XO's server. I haven't had time to research this further, but the quick and dirty fix- shut down any VPN connections- works for me in the short term.
The details of the VPN connection:
IPv4 Connectivity: Internet
IPv6 Connectivity: No network access
Device Name: WAN Miniport (PPTP)
Device Type: vpn
Authentication: MS CHAP V2
Encryption: MPPE 128
Compression: (none)
PPP multilink framing: Off
Client IPv4 address: [address]
Server IPv4 address: [address]
NAP State: Not NAP-capable
Origin address: (unknown)
Destination address: [address]
550 caused by VPN connection
Moderator: Project members