OAM 11.1.2.4 with Webgate 10g for IIS 7 issue with cookie decryption

Dears,

We recently ran into an issue with OAM 11.1.2.4 Webgate 10g for IIS 7. We had an issue with the old OAM domain, and had to create a new one, so we did, using the same middleware home as the old domain.

After that, I re-registered Webgate 10g on the newly created OAM, with the exact same configuration as the old one, with Primary Cookie Domain left as blank. On IIS side, I also reinstalled the Webgate.

Now, when we try to access a protected resource using that 10g Webgate, we face the below error:

[2015-03-10T12:27:40.157+02:00] [oamnew_server1] [ERROR] [OAM-04020] [oracle.oam.proxy.oam] [tid: [ACTIVE].ExecuteThread: '