Why did I received a notice that the financial capacity in my account is less than 5% above the current margin requirement when my stock positions are fully-paid?

Overview: 

IB will issue a warning message to any margin account approaching a maintenance margin deficiency (and therefore potential forced liquidation of positions).  This message is generated when the Equity With Loan Value (ELV for a stock account = Cash + Stock + Bond + Mutual Fund + Non-US Options) is less than or equal to the Maintenance Margin Requirement * 105%.  The warning message reads as follows: 

ALERT: the financial capacity in this account is less than 5% above the current margin requirement.  To avoid a possible liquidation, please monitor the account to ensure that there is positive excess liquidity.

An account which hold stock positions that are full-paid (i.e. no cash debit) remains susceptible to liquidation if the account falls into deficit and the loan value of the stock is insufficient to cover the debit.  This is often the case, for example, when a margin account holds positions subject to 100% margin and a cash balance of $0.  In the event the account is assessed a fee, such as commission, monthly minimum activity or market data subscription, a negative cash balance would results and IB would not be able to extend loan value against these securities to support the debit balance. The account would therefore be subject to a liquidation in an amount sufficient to cover any cash deficit.

Accordingly, the recipient of this warning message may wish to maintain a cash balance in an amount sufficient to cover any potential charges to the account and to avoid a forced liquidation.