I'm able to successfully register an SOE that was originally developed for ArcGIS Server 10.0 on 10.3.1, but when I try to enable the SOE on a map service, it fails and throws the error : ClassFactory cannot supply the requested class. My assumption based off the lacking error message is that a library/dll is not being placed correctly somewhere but the message doesn't say what class, or what directory it's looking in for it.
Can someone tell me what happens after you add an extension in Server Manager? Does it take dll files in the SOE bundle and copy them to the GAC, ArcGIS Server install bin directory, or somewhere else? I've been spinning my wheels on this for 4 days. I've tried manually placing all referenced dlls in the GAC manually at the suggestion of the esri support tech, but that doesn't have any effect and I feel like they are guessing anyway. I know the SOE works because it's running in production on a 10.0 version of ArcGIS Server.
What needs to be done to reuse this SOE on 10.3.1. Also, I've ensured that the extension support was installed as part of the ArcGIS Server installation - I know that was the problem for some with this error. Also, ESRI.ArcGIS.SOESupport (v10.3.0) is in the GAC.