When attempting to import a domain in the Symantec Endpoint Protection Manager (SEPM) from Admin > Domains, you receive "Unexpected server error [0x10010000]" and the domain fails to import.
When you export a domain from the SEPM, a temp folder is created in \Program Files (x86)\Symantec\Symantec Endpoint Protection Manager\data\temp. This folder is needed in order to import a domain into the SEPM. If the SEPM you are attempting to import the domain on has never exported a domain, the folder will not exist and a will result in an unexpected server error.
Export a domain from the SEPM before you attempt to import a domain. You can export a domain by going to Admin > Domains > Export Domain. Alternatively, you can create the missing temp folder in \Program Files (x86)\Symantec\Symantec Endpoint Protection Manager\data.