I could not see anything obviously wrong, so generated my own small data set and tried your COMPUTE command. It worked. See below:
NEW FILE.
DATASET CLOSE ALL.
DATA LIST LIST / SQ_FOODSELECT_M06 SQ_EATDURE_M06 .
BEGIN DATA
1 2
3 4
5 6
END DATA.
COMPUTE super_variable=(.02407*SQ_FOODSELECT_M06) + (.00171*SQ_EATDURE_M06).
LIST.
OUTPUT:
SQ_FOODSELECT_M06 SQ_EATDURE_M06 super_variable
1.00 2.00 .03
3.00 4.00 .08
5.00 6.00 .13
Number of cases read: 3 Number of cases listed: 3
This suggests to me that there might be something funny going on in your dataset. Do you have string variables where you should have numeric variables, for example?
HTH.