SSRS without domian

I have inherited a 10.2.500.4 system that is not on a domain. Everything functions within application outside of SSRS deployment. Support tells us we need a domain, yet along the way someone in the process stated no need for a domain. 2 servers involved also.
Error is
System.Web.Services.Protocols.SoapException: The user or group name ‘XXXX\epicorservice’ is not recognized. —> Microsoft.ReportingServices.Diagnostics.Utilities.UnknownUserNameException: The user or group name ‘XXXX\epicorservice’ is not recognized.

Lot of talent in this group any ideas?

Interesting…

https://social.msdn.microsoft.com/Forums/sqlserver/en-US/30adac15-9a38-4994-94a7-070595f8a733/the-user-or-group-name-mydomainmyuser-is-not-recognized?forum=sqlreportingservices

See bottom post. That might be it.

My guess is that the reporting services was setup at one point of time or the server was joined to a domain.