You receive this error because the webcam is not recognized by your computer or by the software. In order to solve it, I suggest you update your webcam drivers. Navigate to Dell Drivers & Downloads page, identify your computer model, select your operating system and download the webcam files.
After that, press Windows + Pause/Break key combination and open Device Manager. Expand the Imaging devices list, right-click on the webcam driver and select Update Driver Software. Use the Browse option to navigate to the downloaded package, select the driver and install it following the on-screen instructions.
If you still receive the error, try applying the solution from the official Dell forum.