iMovie supports most tape based cameras. With iMovie 9 the imports are usually successful. However, with iMovie 10 importing from tape can be somewhat hit or miss. Many problems relate to defective cables or adapters. You want a firewire connection from camera to Mac, using whatever adapters are necessary. So the first thing is to check your cable and adapter connections.
Apple recommends to import photos and videos into the Photos app for use in iMovie, rather than directly into iMovie. You can then access the videos from the Photos sidebar item in iMovie. You can also use the Image Capture app on your Mac to import to a folder on your desktop. Importing into QuickTimePlayer also can work, although it would come in as one long clip without scene breaks.
Another thing you can try is starting the camera playing once connected, and then beginning the import.
-- Rich