What happens if fixed or floating charge becomes invalid?

1- Charge becomes invalid if: Floating charge: 12 months period Fixed charge: 6 months period ...of commencement of liquidation period. (note: this part is clear, but 2 part is not clear) 2- What I cant able to understand what does that mean by - invalidity of charge, and why liquidator would try to prove invalidity? Its bit confusing. What Im guessing is - liquidator proving invalidity hence the charge wont classed fixed or floating, - and it doesnt get any priority in asset distribution in liquidation - and goes to other category for this, thus it goes in favor of issuer or company Kindly answer my this confusion, I look forward to it, and would really appreciate your help. Thanks Sir!