How can I determine lysozyme activity？

[angelsmile]

Hello，Did somebody use EnzChek Lysozyme Assay Kit(invitrogen,molecular probes)? I meet some difficulty in determining lysozyme activity using the EnzChek Lysozyme Assay Kit(invitrogen,molecular probes). the fluorescence of samples is very low and out of standard curve. I dont know why. principles of kit are as follows:

The EnzChek® Lysozyme Assay Kit (E-22013) provides
researchers with a sensitive assay to measure levels of lysozyme
activity in solution. This fluorescence-based assay can detect
lysozyme activity down to 20 U/mL (Figure 1). The assay
measures lysozyme activity on Micrococcus lysodeikticus cell
walls, which are labeled to such a degree that the fluorescence
is quenched. Lysozyme action can relieve this quenching,
yielding a dramatic increase in fluorescence that is proportional
to lysozyme activity. The fluorescence increase can be measured
using any spectrofluorometer, mini-fluorometer or fluorescence
microplate reader that can detect fluorescein (Figure 2).