User or Group is not recognised error using Forms Authentication

Question

Hi Guys,
Hope you can help; I'm having a bit of trouble adding new users/ groups to my report server.
My current set up is SSRS 2008 utilising forms authentication with single sign- on and am trying to set permissions on a folder level. 
I've checked that the server is pointing to the correct database and that this database is up to date (has all relevant roles, users etc...) but whenever I go to add a new user/ role (site settings --> security) I get the following error:
The user or group name 'Users' is not recognized. (rsUnknownUserName) 
I've also confirmed the roles/ users that I'm trying to add are in the database
I should add that I'm new to this SSRS malarkey so let me know what information you need and I'll find it out for you.
Thanks!

Answer 1

Hi Donpisci,
The error “The user or group name <name> is not recognized (rsUnknownUserName)” means the Report Server cannot find the user from domain or local users or groups of report server. Reporting Services stored users with users’ SID. After we type a username
in the username textbox, the Reporting Services will use the method “LookupAccountName” in Windows API to get the user’s SID.
You can refer to the link below to download the application, and then run the application. Type the user name in the username textbox, and then click “Find” to check whether you can get the SID.
http://cid-3c7e963ff6ccd974.skydrive.live.com/self.aspx/.Public/GetSid.exe
In addition, you can disable firewall temporarily.
Regards,
Heidi Duan
Heidi Duan
TechNet Community Support