Given that the original post is 7 years old and no one has had any suggestions all this time, I suggest you contact MadCap Tech Support for assistance. Sorry that I myself can't help with this.
Nita
RETIRED, but still fond of all the Flare friends I've made. See you around now and then!
I don't think it is related to csh.js. If you get this error, it means Flare can connect to your server, but it can't find the destination (directory) that you want to upload to and csh.js is just the first file that Flare tries to upload before it hits the error (my error was the same).
The issue is most likely that the Destination > Directory field in the Destination file in Flare is not configured correctly.
In my case, I was trying to upload to "public_html/<subfolder>". However, my connection details (combination of FTP server and username) were already connecting to inside the public_html folder, so Flare was looking for a subfolder called public_html... and that doesn't exist, so Flare can't continue the publish action. When I reset the Directory field to just the subfolder name that I wanted to use (and had already set up on my server using my hosting UI) - everything worked fine, published ok.
So, if you get this error, try reconfiguring your Directory field in the Destination file in Flare.