Problem using DSP builder output block with simulink unbuffer block

The problem is that you haven't used DSP Builder blocks between the Input and Output blocks. DSP Builder does not know how to synthesize most simulink blocks (exceptions are some virtual blocks like Goto and From).

The error is quite cryptic but basically it's saying that there the Output block expects one type while the block feeding into it is giving it another. This is because DSPB blocks use their type which allows them to have very large bit-widths. It also has the advantage of making illegal combinations of blocks obvious (albeit the error messages aren't the most helpful).

(If you have your own HDL you can move the simulink blocks inside a subsystem, wrap them in HDL Inputs/Output blocks and add an HDL Entity block pointing to your own HDL, but of course then you have to write your own HDL... probably not what you want).