Entity Framework - Cannot insert explicit value for identity column in table 'LeistungGruppe' when IDENTITY_INSERT is set to OFF

Entity Framework - Cannot insert explicit value for identity column in
table 'LeistungGruppe' when IDENTITY_INSERT is set to OFF

i'm trying to add an EntityObject to my database by calling
AddToLeistungGruppe.
LeistungGruppe in this case is my Table with Primary_Key LeistungGruppe_ID
with Identity true and Identity increment 1 and seed 1.
I search alot for this issue and alot of People got he same error. They
were told to simply set StoreGeneratedPattern to Identity and this would
solve the Problem.
I tried it out and still got the same issue. I'm new to the Entity
Framework and have no idea about how to solve this Problem.
Somehow i think the model isn't updated propably because even if i Switch
arround These Settings i'm getting the same error over and over again.
Every help is appreciated.
PS: sorry for my bad english
Thanks in advance!