Why getting CX_SY_ARITHMETIC_OVERFLOW when table reduction of type f

Need help!

I get an exception in subj when exec the command like

sum = REDUCE f( INIT amt = 0

FOR ln IN GROUP grp
NEXT amt = amt + ln-sum )

All the types are f. The maximum value is 1E+8. Numer of values is 38.

Why this happens? And how to avoid this?