"missing a temporary folder" message for header image upload

I’m fairly new to WordPress, and have tried several times unsuccessfully to upload images from my computer to use as headers. I’m using the Weaver theme. I keep on getting the message ‘missing a temporary folder’, but am not being told what to do about this.
Searching for this problem on the forums brings up different responses.

I had WordPress installed through my host (GoDaddy); I didn’t install it manually. I use FileZilla as my FTP client.

Advice on what to do would be appreciated.