cannot convert yyyymmdd to yyyy-mm-dd - arithmetic overflow error
The column is actually stored as an int, and it means something different in datetime, so you'll need one extra step in your CONVERT:

CONVERT(DATETIME, CONVERT(CHAR(8), next_run_date), 112);


To show why you can't do this directly to an int:

SELECT CONVERT(DATETIME, 0);
SELECT CONVERT(DATETIME, 1);


When it's an int, it's actually the number of days since 1900-01-01.