This trial is conducted in Europe. The aim of this clinical trial is to compare the pharmacodynamics (i.e. the glucose-lowering effect of the study medication over the entire observation phase from the time of administration and the efficacy period) and the pharmacokinetics (i.e. amount of the study insulin that can be determined in the blood) of a treatment with biphasic insulin aspart 30 (BiAsp 30) administered once, twice or thrice daily and biphasic human insulin 30 administered once daily in type 2 diabetic subjects