What davidrw said about changing the split statement is bound to be the solution. I'd also point out this part of the error message:

... at meanStddev.pl line 6, <FILE> line 1
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The message tells you not only where in your script you had a problem (line 6 of the perl code: $sum[$i]+=$fields[$i];), but also which line of data in your input data file had just been read when the error occurred. That is, the initial space is in line 1 of the data.