You should use normal double quotes (also known as straight quotation marks) in AFL to surround strings instead of the ones (known as curly quotes, typographic quotes, smart quotes, curved quotes, or book quotes) that you probably copied from some website and pasted in your editor.
for( i = 0; i < BarCount; i++ )
{
if( Buy[i] )
{
PlotText( "\nBuy:" + L[ i ] + "\nT= " + ( L[i] * 1.005 ) + "\nSL= " + ( L[i] * 0.9975 ), i, L[ i ] - dist[i], colorGreen, colorWhite );
}
}