red dotted wire instead of solid black wire problem in simulink

I am using Simulink, simRF, DSP system toolbox and Communication system toolbox in my design, while i am connecting blocks with each other many shows red dotted lines instead of solid black lines although the blocks are taken from same library like while connecting mixer block output with the RF low pass filter input, shows a red dotted lines.

Answer 1

[Azzi Abdelmalek]

Red dotted lines means you can't connect these blocks. Read this link http://www.mathworks.com/matlabcentral/answers/14998#answer_20419