We also have EOL old product (but it' works fine!), and have some problem :(
Product: Cisco IronPort C150 Messaging Gateway(tm) Appliance Model: C150 Version: 7.5.2-014 Build Date: 2012-03-06 Install Date: 2012-03-06 23:35:48
I think, cause maybe in internal date/time variables of AsyncOS. If set date/time manually, for example, to 12/30/2017 - GUI works correctly.
Upgrade AsyncOS to latest possible version resolve the problem:
Product: Cisco IronPort C150 Messaging Gateway(tm) Appliance Model: C150 Version: 7.6.3-019 Build Date: 2013-06-09 Install Date: 2018-01-29 14:04:14
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