This is an open label phase I/II study dose escalating study to investigate safety, tolerability, and preliminary efficacy of the trifunctional anti-HER2/neu x anti-CD3 antibody ertumaxomab in patients with HER2/neu (1+/SISH positive, 2+ and 3+) expressing solid tumors progressing after standard therapy. The primary objectives of the study is to assess the safety and tolerability of ertumaxomab in order to determine the maximum tolerated dose (MTD) and to establish a recommended dose (RD) for further development.