XIRR Calculation Error

The problem is with that first date being a net-zero transaction. Try filtering out such days.

IRR =
VAR Summary =
    SUMMARIZE ( Table, Table[Transaction Date], "@Amt", SUM ( Table[Amount] ) )
VAR FilterZeros =
    FILTER ( Summary, [@Amt] <> 0 )
RETURN
    XIRR ( FilterZeros, [@Amt], [Transaction Date] )

The first transaction is the culprit again. Having a small value like that as the first transaction is destabilizing and the XIRR function is not very robust. I don't know of a good general solution to fix this deficiency but I have applied some tricks in my reports that sometimes work.

For example, if you modify the data slightly to invest an extra $100 for one day so that instead of -1 on 9/1/2009 you have -101 on 9/1/2009 and 100 on 9/2/2009, then XIRR does converge. This modification does not materially change the result but it improves the stability of XIRR convergence.