Error messages for Mixed Effect Model in SPSS?

#1
I keep getting error messages:' The levels of the repeated effect are not different for each observation within a repeated subject.' when performing Mixed effect model in SPSS.

I have two groups of participants X and Y who performed two sets of tasks i.e. A and B. Group 1 has 12 subjects, Group 2 has 16 subjects. Each subjects performed 12 trials in each of the tasks although there are some missing data. I'm interested in the mean differences in latency (Dependent Variable) between the two groups and tasks (i.e. standard Mixed Plot ANOVA design) and would like to use Linear Mixed Model to analyse the data in SPSS. I labelled Task as Repeated Measures factor (same group of participants in both tasks), Group as Fixed Effect, and ID as Random Effect.

I really appreciate if anyone can offer me some advice as to whether I've organised my data appropriately for Mixed Effect Model in SPSS or whether it is even possible to performed the procedures with my my data.

I've organised my data in this manner:

ID Group Task Latency
1 A 1 283
1 A 1 357
1 A 1 457
2 A 1 289
2 A 1 354
2 A 1 892
3 B 1 283
3 B 1 357
3 B 1 457
3 B 1 289
4 B 1 354
4 B 1 892
4 B 1 283
1 A 2 283
1 A 2 357
1 A 2 457
2 A 2 289
2 A 2 354
2 A 2 892
3 B 2 283
3 B 2 357
3 B 2 457
3 B 2 289
4 B 2 354
4 B 2 892
4 B 2 283