Revenue Generation Error - Null GL# 101 key flexfield is not allowed

When generating draft revenue from usages, I am receiving an AutoAccounting error.  I have PA: Debug mode set for my user and the only error message I received is Null GL# 101 key flexfield is not allowed.  I've validated that AutoAccounting rules have been defined for Usage Revenue, Cost, Cost Clearing and that Revenue/Invoicing AA rules have been defined.  I've confirmed that Revaluation is not checked in Implementation Options, therefore Gain/Loss Accounts are not required.  Cross validation rules have not been defined yet in the general ledger and when I manually enter the account via journal entry, the combination is