FLAASH produces weird peaks

I am applying FLAASH to atmospherically correct and convert to reflectance a hyperspectral image acquired by our airborne system. The problem is that FLAASH (using ENVI) outputs an image where all spectra peaks around 763nm. all spectra have the same peaks regardless of the observed materiel. the Image bellow is a spectrum of a Spectralon that should have 36% reflectance.

My input image to FLAASH is Radiance acquired by the airborne system but actually has a weird problem too. Spectra regardless of the observed material drop in a negative peak at the same wavelength. Here is an image of the same Spectralon before applying FLAASH :

I am starting to think that this is a camera problem. Does anyone know where this problem is coming from? or suggest any ideas?

PS : I’ve applied FLAASH with different parameters but the peaks are always there.