Your problem is that your initial values for steady state computation are not good for different parameters. Hence, during estimation, Dynare often cannot compute the steady states. See e.g. [Bayesian Estimation and Steady State Updating) and “Remark 14 (initval vs. steady_state_model vs. steadystate-file)” in sites.google.com/site/pfeiferecon/Pfeifer_2013_Observation_Equations.pdf.
In your case, try using a different solve_algo by putting e.g.
before your estimation command.
Finally, using only two observations is odd.