The error message "Policy installation failed on gateway" and its predecessor "Load on module failed" indicate that the policy passed SMS verification and was compiled & successfully transferred to the gateway, but the atomic load of the policy into the running firewall kernel failed. These are frustratingly generic error messages for the simple reason that the SMS has no idea why the load failed, only the gateway does. Debugging of this problem needs to take place on the gateway. The linked SK below lays out some of the different situations that can cause this, but in my experience it generally boils down to one of the following:
1) Memory or other resource shortage on the gateway, in the case of a long-term memory leak a reboot of the gateway may help
2) The compiled policy is "corrupt" and should not have passed verification in the first place on the SMS. This can be caused by damaged files referenced during policy compilation on the SMS, or the user being improperly allowed to enable settings/features that the target gateway software version cannot understand or support
3) Error in policy compilation not caught by the SMS such as the same variable getting included in the compiled policy more than once, or conflicting settings for the same object
4) Possible corruption on the gateway, once again a reboot may help
sk33893: 'Installation failed. Reason: Load on Module failed - failed to load security policy' error...
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