Foreign key constraint with dbo.aspnet_Membership", column 'UserId' when inserting new item using Linq detail view

The INSERT statement conflicted with the FOREIGN KEY constraint "FK_JobList_aspnet_Membership". The conflict occurred in database "C:\DOCUMENTS AND SETTINGS\QI\DESKTOP\JOBPOST\APP_DATA\ASPNETDB.MDF", table "dbo.aspnet_Membership", column 'UserId'.The statement has been terminated.
My FK_JobList_aspnet_Membership setup is
Primary table(aspnet_membership) foreign key table(JobList) use column UserId(uniqueidentifier) JobList has its auto indexable primary key int JobId.
I don't understand why the exception happens, since i use membership service after user lo ...