Having it checked with the previous engineer, you were getting an input / output related related error, while adding the ACL policy. There is a similar issue, so in order to mitigate the issue previous engineer requested you to perform reboot of the appliance and then try adding ACL policy.
This will help us to narrow down the issue and to find the cause of the same.
Please update us with the status after performing the reboot, if that fixes the issue.