MS-DOS Doom WAD W_CacheLumpNum Issue

[NiTROACTiVE]

So I'd like some help when it comes to getting the WAD Illuminatus (which is the WAD I'm getting really close to finish as of this post) to work on DOSBox. I keep getting the W_CacheLumpNum error as I try to play the WAD in DOSBox, as custom flats show up in certain maps. I attached a picture of how the custom flats were inserted into the WAD. What's weird is that I do believe that I didn't get this error before in the past. I am also trying out this WAD on Doom II v1.9, so could it be a version issue? Either way, I would like some help.

[Linguica]

make sure your custom flats are at the very start of the WAD and surround them with FF_START and F_END not FF_END.