We conducted a qualitative research of case studies based on think-aloud protocols. The aim was to carry out in-depth analyse secondary students' cognitive difficulties appearing in early stages of transfer processes in problem-solving. The task was to relate several source problems to a target problem, in order to solve it effectively. Source and target problems had different Surface and/or Structural similarities. In this paper, the solvers' high or low Familiarity with the problem stories on transfer processes was also focused on. Two emergent instructional phenomena are described, both associated to specific students' cognitive obstacles to achieve success in solving the target problem: the "Screen effect" and the "Sisyphus effect". The obstacles were harder for low Familiarity problems.