While opening the new project, I am getting the error like "Error downloading the following files: mcusAds.json(HTTP Access Forbidden". Kindly help me.

[Cartu38 OpenDev]

Which STM32CubeIDE release are you relying on ?

If old one please update ... (current is 1.6.0)

If recent release maybe local network issue. In order to workaround waiting for alive connection have a try to:

Would advice to come back to default setting as soon as possible then. If not you are going to possibly miss some important update at a time.