This can be for a number of reasons. Please verify that the analog camera is correctly connected to the capture device, and that the device is correctly installed on the computer:
The video capture device must be Direct-X compatible. Some multi-channel DVR cards are not compatible with Direct-X and will therefore only work with their own custom software, and not with third party software like Zone Trigger. Most TV-tuners will have no problem.
Direct-draw and Direct-3D are part of Direct-X but do not enable compatibility with video capture (Direct-Show).