Cust/Vend logon to EP

Hi, My client is experiencing some strange problems in Enterprise Portal when she tries to connect using a Cust/Vend web user (E.g. the cust web user is attached to a regular axapta user which belongs to 2 user groups: EP_Cust and EP_Ext). She only get’s this error for the Cust/Vend, not also for Admin. The error says: AxaptaComConnector.Axapta.1 Company accounts ‘dat’ does not exist. She is using Axapta 3.0 SP4/XP/SQL Server 2005 I have done the same settings on my instance and it is working well. I am using Axapta 3.0/Win2003Svr/SQL Server 2000. Has anyone else see this? Please advice.