Calculating NDVI (Normalized vegetation Index) using Landsat8 images in ENVI 5.3

The normalized difference vegetation index is a simple graphical indicator that can be used to analyze remote sensing measurements, often from a space platform, assessing whether or not the target being observed contains live green vegetation. Range: -1 to +1 Vegetated areas will generally yield high values for NDVI because of their relatively high NIR reflectance (0.7 - 1.1 μm) and low visible reflectance (0.58 - 0.68 μm) NDVI shows as a high value for denser vegetation, while the NDVI is very low in desert, or non-vegetation regions.

[Mrkrabs]

ENVI is telling me it is unable to read my MTL file as Landsat GeoTIFF, is there something I can do about this to get it to work