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.' Can anyone offer me some advice whether I can perform Mixed Effect Model in SPSS with my data or I have organised my data correctly?

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 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'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
 

ondansetron

TS Contributor
#2
Without having time to go into the rest of your post, it appears that comparing the latency values between task 1 and 2 in a given group (say, A), the values are identical. I'm guessing that A,1 and A,2 are supposed to be the repeated measures of the latency for the same experimental unit. This seems to be what the error is telling you.

In other words, Participant 1 in group A has the exact same latency values for Task 1 and 2.

You should determine if this is an input error or if this is your actual data. If the former has occurred, re-enter your data correctly. If the latter, why are scores identical between Task for a given participant in a given Group?