I have same code that, I'm pretty sure works in version 9, but not in version 10.
Unfortunately I dont have v9 anylonger.
This code is from an Notebook created with v9 and now, for some reason I can't evaluate it with version 10.

    in = 2 UnitStep[t - 20] - UnitStep[t - 500];
    tMax = 100;
    time = {t, 0, tMax};

    Wp23 = TransferFunctionModel[{{{E^((-2) s)}}, (1 + 2 s)^5}, s]

    thisWcA = TransferFunctionModel[{{{0.8908858730832925 (1 + 19.096 s)}}, 
      19.096 s}, s]

    outA = OutputResponse[
      SystemsModelFeedbackConnect[
       SystemsModelSeriesConnect[thisWcA, Wp23]], in, time]


What I get from this is just a huge list of errors.
Does someone know where my error is, or is it realy the version thing?