It's the SUM part that is preventing the drill-down.
You probably don't need SUM based on what the rest of the formula contents are, and may be able to use =-ADGET("gldata.BAL",$A10) to show the negative balance of the account(s) in cell A10 as of the selected fiscal period and year.
It may be desirable to see if your financial statements require 'cleaning up' to enable functionality such as this. For example, the ADGET formula has essentially been superseded by the GLAMT formula (though ADGET still works OK). If this is something worth pursuing, your Adagio consultant would be happy to assist you.
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Softrak Tech Support