opencv_error_code-215_channels

Hi, Does anyone know why I'm getting the error message below : Thanks, OpenCV Error: Assertion failed (channels() == CV_MAT_CN(dtype)) in copyTo, file /home/.../opencv/opencv-3.1.0/modules/core/src/copy.cpp, line 257 terminate called after throwing an instance of 'cv::Exception' what(): /home/.../opencv-3.1.0/modules/core/src/copy.cpp:257: error: (-215) channels() == CV_MAT_CN(dtype) in function copyTo