Installation failure using Utility on Kubuntu for Sansa Clip+

[pwabrahams]

I've been trying to update my Rockbox firmware using the Utility under Kubuntu. My device is a Sansa Clip+.  I get as far as extracting the file, but then I get the message "Creating output file failed".   I've gotten this to work in the past, but I don't know what's different.  I'm trying to install the archived build r30258, but I have the same problem even if I try to install the stable build 3.9.  I've successfully (I think) reinstalled the bootloader.

How can I get past this?