Did you change anything about your setup between the last time you used the scanner and the time the black bar started appearing? Are you scanning photos or text and does that make a difference?
A few years ago, while using a much older scanner, but also VueScan, I had the same problem. Never did get it fixed, and, as the scanner was an old SCSI, I finally bought the scanner you have. I've not had the same issue.
Do you have another scanning software you could try? The scanner comes with ScanGear, I believe. And I know VueScan had an update just yesterday. And by the way, I updated my own VueScan a few days ago and it worked fine with my scanner. I would try upgrading the VueScan to see if that helps.
And this is off your topic, but I'd love to know if you have the same issue I do. Are you able to install OmniPage SE, which is OCR software that comes with the scanner? I cannot. I get error messages. And ScanSoft wants $10 for tech support. That was when I discovered I could upgrade my VueScan, which added OCR a while ago. It was fine for my minimal (at this point anyway) needs.
But boy, does OCR software for Mac stink.