GE 90-30 PLC Sequence Store-failure

We have GE Plc 90-30 CPU 351, working in an injection machine. recently when we switch off the machine for more than 1 hour the machine stops in fault mode. the fault table shows PLC "sequence store failure". after clearing the error the machine works fine. the machine check for the program and plc data each time it starts. we checked the communication cables and they are ok .
any suggestion please

Your description suggests a problem with the battery since the fault only happens after the unit has been powered down for longer than an hour. There is a capacitor of the CPU mother board that will retain RAM memory for a brief period after primary power is removed, even if the battery has failed.

But there is no battery message and the bat led is ok.

Exactly what I expected you would report. The symptoms are consistent with a battery problem even if you aren't getting all the symptoms you would normally get with that particular fault. It may also suggest problems with flash memory. Is the hardware configuration set to load program or data from flash on power-up? Is there anything stored in flash memory?
What is the timestamp on the fault? Does it coincide with when the PLC is powered up after having been off for an hour or more?
You could try setting the "Ignore fatal faults" parameter in the CPU configuration to "Enabled".

yes the hardware configuration is set to load program and data from flash on power-up

Then I would try downloading the program to flash again. The fault may be generated when the program stored in flash is transferred to RAM.

once we clear the fault table and set the plc to run every thing is fine which suggests that the program is ok. isn't it?
I think the best thing we do is to change the battery first since the problem is related to power.