Ertheia cant use Grades itens (D,C,B etc) after 4th class REV 1987.
The item Expertise Passive Skill Vanish after the class change, as result you cant equip any item.
Edit: This cloud be the fix ?
Add the line: <skill skillName="Expertise" skillId="239" skillLvl="1" getLevel="1" /> to the Eviscerator.xml ?