I saw you using values close to 1.00
a thing is: 1.00 is the size of a whole image.
shader texture positions aren't counted in pixels, but floating point values from 0 to 1.
0 is the left, 0.5 the half, and 1 the right of the image.
your blurring taps are moved so far, that they are getting out of range, at least, they leave the original pixel.
for blurring, use values from 0 to 0.01 as someone said before