You have a few errors in the code.

• The definition of coeficientOfVariation[val_] is missing an additional f.
• Sqrt[val["PathLength"]] should be Sqrt[Length[val]].
• Mean[val["PathLength"]] should be Mean[val].

It is not so obvious what your data are:)

Lets say you have computed your mean data and errors to be:

mean = {7.43, 8.83, 6.06, 13.8};
errors = {4, 3, 2, 1};

then you wrap Around to your data:

data = Apply[Around, Transpose[{mean, errors}], 1];

and BarChart it:

BarChart[data, ChartElementFunction -> "GlassRectangle", 
 ChartStyle -> "Pastel"]

which gives:

One way to include error bars in BarChart is with Around:

standardError[val_] := StandardDeviation[val]/Sqrt[Length[val]]
LRed = {7.43, 8.83, 6.06, 13.8};
stdErr = standardError[LRed];
LRedAround = Map[Around[#, stdErr] &, LRed];
BarChart[LRedAround, ChartElementFunction -> "GlassRectangle", 
 ChartStyle -> "Pastel"]

which gives:

Out[28] and Out[29] have not evaluated standardError and coefficientOfVariation which means those functions have not been defined. Did you evaluate the cells that contain the definition?