Insert Permission Denied After Granting Permission

SQL Server 2005 anomoly?
In SQL Server Management Studio I granted specific permissions to user "A" to do Select, Insert, Update, Delete on Table "B" -
When I logged on as User "A" and attempted the Insert imto table "B" I got the following error:
"Insert Permission Denied on Table B, Database C, Schema dbo"
Is this a problem with the dbo schema?

Then I went back and created a stored proccedure "D" with the exact same Insert statement inside the procedure. I granted User "A" execute permission on the stored procedure "D".
I then logged on as User A and executed Stored Procedure "D". No Problem - stored procedure executed fine with the Insert.
I attempted the Insert statement again - straight SQL - as User "A" and got the same error as above ("Insert Permission Denied.....")
Strange behavior - cannot do a SQL. Insert even though user has permissions but can execute a store procedure with the same Insert statement.
What gives?