Odd upload problem

Not sure what this means - for the first time I am getting an upload message warning:
can't change directory to public_html/index_htm_files/Big export from Master_htm_files/Ackley Bell Jar Evelyn Ackley Speckman.jpg: Not a directory
I have no idea what this means. anyone?

What program and version are you using (what does the top line say in Help > About)?

In the Publish tab of Web Properties, what have you entered for the 'Sub-Folder Path'?