It's quite possible that the Dazzle unit is deliberately limited to work with only the Pinnacle software that came with it. It may not allow use by any other software. Vegas' capture utility is also fussy about only capturing from firewire devices and doesn't like to talk to USB devices. Can you capture successfully with the Pinnacle software? If so, do that and save the files. You can then open and edit the resulting files in Vegas.
Dazzle DVC100 Video Device last downloaded: 17.1.2018 - 2018 version. Download Rating: 83%. Device drivers: Dazzle DVC100 Video Device - driver download. This page contains the list of download links for Pinnacle Sound Cards & Media Devices. To download the proper driver you should find the your. Dazzle DVC100 Audio.
I'd also suggest you look for almost anything besides the Dazzle. Sola-larm 835t Manual. Historically Dazzle devices have been some of the most absolutely awful pieces of hardware ever made.