fatal:Subscript out of range, error in subscript #0

I just wonder, why did i get this error message when i simply use
the my stat_dispersion function as follow:

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
load "./stat_dispersion.ncl"

begin
[snip]

 opt = True
 opt@PrintStat = True
 stat = stat_dispersion(temp(:,{10:50}), opt )

end

----
the error :
fatal:Subscript out of range, error in subscript #0
fatal:Execute: Error occurred at or near line 92 in file
./stat_dispersion.ncl
----
My variable is:
Variable: temp
Type: float
Total Size: 30240 bytes
            7560 values
Number of Dimensions: 2
Dimensions and sizes: [lat | 21] x [lon | 360]
Coordinates:
            lat: [ -10..  10]
            lon: [-180.. 179]
Number Of Attributes: 6
----
I attached the "stat_dispersion" file here.
Thank you  for any response.
Xi

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