SQL Error when trigger fires in SQL Server 2008 R2

Hi.  I am trying to use triggers to automatically update LastUpdated (datetime) and LastUpdatedBy (varchar(20).  

I wrote this trigger for LastUpdated and it works fine.

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER TRIGGER [dbo].[trEmailGroupMembersLastUpdated] ON [dbo].[EmailGroupMembers]
FOR UPDATE 
AS
UPDATE EmailGroupMembers SET EmailGroupMembers.LastUpdated=getdate()
FROM EmailGroupMembers INNER JOIN Inserted ON EmailGroupMembers.EmailGroupMemberID= Inserted.EmailGroupMemberID

Select allOpen in new window

However, the trigger I wrote for LastUpdatedBy does not work.  

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER TRIGGER [dbo].[trEmailGroupMembersLastUpdatedBy] ON [dbo].[EmailGroupMembers]
FOR UPDATE 
AS
UPDATE EmailGroupMembers SET EmailGroupMembers.LastUpdatedBy=(ltrim(rtrim(substring(suser_sname(),(5),len(suser_sname())))))
FROM EmailGroupMembers INNER JOIN Inserted ON EmailGroupMembers.EmailGroupMemberID= Inserted.EmailGroupMemberID

Select allOpen in new window

I get this error from the Access 2010 frontend form when it tries to save to SQL Server.  

I have tried different ways to write the trigger but I cannot avoid this error.  Does anyone know what I am doing wrong?

Thanks,
Alexis