LubeckTech79

I am trying to play on a server named A Valkyrie's Pride and am having a problem. When I try to join the server I get the error message that my version has "PBR" that is not recognized by the server and refers to my game install files. Is it referring to PBR Shaders and if so can I safely remove them?? Also I am new to this game and would like to know what the term "Vanilla Servers" refers to.