If iMovie does not recognize or controls the camera

First check the following

If the Fast User Switching feature is enabled in OS X, make sure no one else is trying to use the same camera from another user account. For more information see the article iMovie: Fast User Switching and control a DV camcorder.
If it is a tape-based camera, checking that it is not tape Hi-8 or Digital-8. Make sure that the movie recorded is not in Hi-8 format. Movies recorded in Hi-8 work with some DV camcorders, but not with iMovie '08 and later.
If these steps do not resolve the problem, identify the type of device you have available in the list below, and follow the steps described in the section.
DV, HDV and other connected via FireWire
Camcorders that record to DVD, hard drive or flash memory
built-in FaceTime HD camera or iSight camera
DV and HDV

Make sure that your DV camcorder is connected to the computer's FireWire port and that the camera is turned on.
Note: Many DV cameras are equipped with USB and FireWire (also known as i.LINK or IEEE 1394). On DV camcorders, USB is normally used for downloading images but not video. To work with iMovie, use the FireWire connection.
If the camera is turned on and connected via FireWire, to reestablish the connection follow one or more suggestions from those below.
Please reboot the camera.
Unplug the FireWire cable from your computer and then reconnect it. Repeat the operation also on the camcorder. If the camera is connected through a FireWire hub, try connecting directly to the computer.
Make sure that the tape in the micro spy camera is working. Eject and reinsert the tape to make sure it is properly inserted. Try using a different tape.
Quit iMovie, then start it again.
Restart your Mac.
Try to use another FireWire cable or try to connect the camcorder to another Mac that has iMovie.
Damaged tape, dirty heads or mixed footage formats may cause the sudden interruption of import from the camera.
If iDVD is running, quit iDVD and iMovie, iMovie and then starts again.
Open System Information to check if the camera is displayed. If the camera does not appear in the USB or FireWire, try resetting the FireWire connection as described in What to do if your computer will not recognize a FireWire or USB device, then try again.
Make sure that no other applications, such as iChat, Messages or other chat applications or for video editing, is using the same camera. Try closing any other applications that may interact with the camera.
For information about connecting and configuring the camera so that it can be used with your computer, see the documentation that came with the camera or contact the manufacturer.
In the documentation that came with your camera or DV device should be available information on locating the FireWire port on the camcorder. Sometimes this port is also called iLink or IEEE 1394.
In order to communicate with your computer, some cameras must be set to "VTR" mode, "VCR" or "DV". If necessary, consult the camera's documentation for information on how to set this mode.
If you are using an analog-FireWire converter (DV deck), in some cases you need to change the device settings by pressing certain buttons or switches on the device itself. Some DV bridges also require the installation of drivers or firmware upgrades to allow control and device recognition. For more information, consult the documentation that came with your DV bridge, or check the manufacturer's website.
Some cameras are switched off automatically to reduce battery consumption. If during import or export the camera suddenly turns off, connect it to the AC adapter
Make sure the date and time of the dv camera are set correctly. If the camera uses a backup battery to prevent the date and time may be reset, check that the battery is in good condition. For more information, consult the documentation of your camcorder and iMovie Article: automatic detection of the scene requires that the camcorder's clock is set correctly.
Some cameras allow you to record at different speeds. Before connecting the camera to the computer, make sure it is set to the maximum speed (SP), even if the footage was recorded at a slower speed. In some models the speed settings can affect the way the camera communicates with the computer. For more information see the documentation of the camera and try to perform some test recordings at different speeds to make sure the recording speed is compatible.