Blanchard & Kahn conditions are not satisfied: indeterminacy.The rank condition ISN'T verified!

[jpfeifer]

Oscilating or alternating IRFs

It means that there is a complex eigenvalue leading to oscillations. Usually, when people have this problem in the forum, it comes from them ignoring the Dynare timing convention and then torturing the timing until the BK conditions are satisfied. When doing so, the correct economic timing is ignored and oscillating IRFs result.