What version of Notification Server you are using?
Probably you have something similar like in this old case? https://knowledge.broadcom.com/external/article?legacyId=TECH226803
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Software QA Engineer 3
Broadcom Inc.
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Original Message:
Sent: 07-08-2020 09:24 PM
From: Bluecoat Support1
Subject: Internal Server Error when creating Detection Rule