I switched from ZoneAlarm to Comodo firewalls this week. I now find that the ftp file upload function built into CoffeeCup no longer functions. The "Transferring files" window opens, but the transfer never happens. Disabling the firewall cures the problem, but that's not something I'd like to do on a regular basis.

Filezilla works fine. The only difference between the two I see in the setups is Filezilla has a blank field for Port number whereas CoffeeCup specifies Port 21 (and will not accept a blank).

Has anybody run into this issue with Comodo and found a way to resolve it?

I, too am using COMODO. Everything was working great in the HTML editor, including the very handy and quick "upload file to server" feature, but after I installed Windows XP Service Pack 3, I now am getting "Error 500 illegal PORT command". I don't know if that's a coincidence or not. Disabling COMODO has no effect for me. Oddly, I CAN use freeftp.exe out of the HTML editor menu (tools>applications>freeftp.exe) to upload my files, and my regular FTP client, FileZilla continues to work properly. Go figure. I am corresponding with the Coffeecup support group, who have opened a ticket on my problem, and I'm continuing to experiment. Nothing successful so far.

UPDATE: Looks like I pulled the trigger a little too quickly. I've discovered my problem. In addition to COMODO, I'm using NOD32 Anti-virus (by ESET), and I had recently updated to the paid version, which I had installed via CD. That's what changed (I had been using the evaluation version that I downloaded from the internet. Apparently, the Coffeecup HTML Editor was tagged as an internet browser, and all the files it was trying to transfer were being processed -- and failing -- by NOD32. I unchecked Coffeecup (NOD32 is now NOT treating Coffeecup as an internet browser), and now everything is working properly. Whew!

Basically, the problem involves setting some rules in Comodo. If you go to the Comodo forums (open the Comodo manager, click on Miscellaneous in the upper right corner and click on browse support forums) and type ftp into the search field you should get a long list of threads talking about this problem. There is one thread that starts out with an overall reply that shows a screen capture of the predefined policies for FTP. To get to the policies, click on firewall - predefined firewall policies - FTP Client - Edit. Then make the policy list look more or less like the picture by editing the existing rules (deleting the description for each rule makes the rule title look more like the picture). You also have to make at least one addition to the global rules (in the Network Security Policy) and the programs involved (in this particular instance coffee.exe and freeftp.exe) have to be trusted and should show up in the Application Rules tab. If you putz with it long enough you should be able to get it to work.