Invalidity of Loan Documents. Any material provision of any Loan Document, at any time after its execution and delivery and for any reason other than as expressly permitted hereunder or thereunder or satisfaction in full of all the Obligations, ceases to be in full force and effect; or any Loan Party or any other Person contests in any manner the validity or enforceability of any provision of any Loan Document; or any Loan Party denies in writing that it has any or further liability or obligation under any Loan Document, or purports to revoke, terminate or rescind any provision of any Loan Document; or