Note the documentation of bollinger input argument Data:
Data for market prices, specified as a matrix, table, or timetable. For matrix input, Data must be column-oriented.
This means that bollinger is expecting one or more columns of data. You've given a row vector, so transpose (.') it:
Data=1:500;
[middle,upper,lower] = bollinger(Data.');
plot(Data)
hold on
plot(middle,'--')
plot(upper,'--')
plot(lower,'--')
