Look at the query which is generating the error.
Look at the columns whose target is an INT.
Of...

This is the same number, formatted as Scientific (left) and General (right).

Duplicate post. See here.

Try this:
SELECT
  ot.HoldingID
,  ot.IndicatorID
,  DateFrom = MIN(ot.HistoryDateTime2)
,  DateTo = MAX(ot.HistoryDateTime2)
FROM #OutputTable ot
GROUP BY
  ot.HoldingID
,  ot.IndicatorID;