A different cyberduck issue

I have made a simple applescript which chooses a file and uploads it to an ftp site using Cyberduck
It looks like this

set theFile to choose file with prompt "Please select a file to upload:" without invisibles
tell application "Cyberduck"
	tell browser 1
		upload file theFile
		refresh
	end tell
end tell

I keep getting this error, however.
“Cyberduck got an error: Can’t make file (alias “sys:Users:pedro:Desktop:papel-a4.jpg”) of browser 1 into type reference.”

Help
Pete O’Connell

Guessing by the error message, you’re trying to coerce an alias to a file; Try upload theFile.

Hi, thanks for the reply.
When I write it as you suggest I get a new error message.

set theFile to choose file with prompt "Please select a file to upload:" without invisibles
tell application "Cyberduck"
	tell browser 1
		upload theFile
		refresh
	end tell
end tell

Gives me this message

“Cyberduck got an error: Some parameter wasn’t understood.”

at the line of my script “upload theFile”

Any more advice is very appreciated
Pete