c3dbfd83_imply_Modbus___Exception_Codes__Meaning
[Exception Code] 08 (08 hex) [Name] Memory Parity Error [Meaning] 
Specialized use in conjunction with function codes 20 and 21 and reference type 6, to indicate that the extended file area failed to pass a consistency check. The slave attempted to read extended memory or record file, but detected a parity error in memory. The master can retry the request, but service may be required on the slave device.
Simply Modbus - Exception Codes
Meaning