Bryce1552,
I receive a similar error message when I try "mat_reloadallmaterials" without having first used "sv_cheats 1", OR without having joined my own server yet. Make sure you (from the main menu) goto Servers>(+)>Start to create your own listen-server on any map (the default one will be fine whatever it is). If you're not on your own server, then "sv_cheats 1" probably won't work (about 99.9%, unless you've actually found a pub with cheats turned on) , and then "mat_reloadallmaterials" won't work (properly). If you had already done all of that and still had those issues, then I currently have no idea. I'll look into it shortly.