Panasonic FP Series Programming Manual page 816

Error flags
No. IEC address
%MX0.900.7
R9007
%MX0.900.8
R9008
Set If
permanently  the specified address using the
index modifier exceeds a limit.
for an instant  a number other than 0 to 31 is
specified for the slot number.
Data transfer within the PLC
815