I have a in-built webcam in my Sony Vaio VGN-FE21M. lsusb shows me the device

Bus 001 Device 003: ID 0ac8:c002 Z-Star Microelectronics Corp.
Visual Communication Camera VGP-VCC1

and it is working within Skype most of the time. Sometimes, however, lsusb shows me the exact same output, but trying to test my cam in v4l2ucp I get the error

Unable to open file /dev/video0
No such file or directory

A reboot fixes the problem but I just can't pinpoint what the difference is between a working and a not working webcam and the time/instance this occurs.

It would probably be a fix if i could unmount and remount the cam, but how can I do this with in-built devices? Any other advice is welcome as well.