The way you are writing the last few arguments to Table
Table[ ...
t1 = to + Delta;
{t1, iL21}, {t1, 0, tmax, Delta};
{t1, iL11}, {t1, 0, tmax, Delta}]
do not match the documentation for Table.
Table[expr, {i, imin, imax, di}]
Perhaps try this instead
z = Table[...
t1 = to + Delta;
{t1, iL21, iL11}, {t1, 0, tmax, Delta}];
which produces a row of three items t1,iL21,iL11 for each t1 and then ListPlot uses the desired columns.
ListPlot[{z[[All, {1, 2}]], z[[All, {1, 3}]]}]
Then
Sqrt[Mean[z[[All, 2]]^2]]
and
Sqrt[Mean[z[[All, 3]]^2]]
will calculate the square root of the mean of the squares of iL21 and iL11
Please check this carefully, perhaps on smaller examples, until you are certain that you trust that this is precisely correct.