Are you, perhaps, carrying the shares of a Money Market Fund as a security (i.e., "shares") rather than simply carrying them as Cash?Do you have a "Linked Checking Account" associated with this brokerage account? If so, that fictitious "checking account" can hold only cash ... as you've noted, you can't hold a security in a checking account.And, elaborate upon what Fidelity accounts (what type of accounts) are involved in this. Because it looks like your 2nd sentence can't possibly be precise. What you did was to transfer cash from one Fidelity account to another.