Cooking Error: Invalid USkeleton supplied

Development Character & Animation
1

Hey all,
im trying to cook my first game but i keep getting this Error:

PackagingResults: Error: Script Msg: /Game/ThirdPerson/Blueprints/MF_Run_Fwd : Unable to retrieve target USkeleton for Animation Asset (/Game/ThirdPerson/Blueprints/MF_Run_Fwd.MF_Run_Fwd)
PackagingResults: Error: Script Msg: /Game/ThirdPerson/Blueprints/MF_Run_Fwd : Invalid USkeleton supplied

I am unsure what is wrong, cause it seems to me that this is refering to the Standart Mannequin Skelton which i didnt touch or adjust (Except for some footstep Triggers).
When I open the refered Animation Squence i do get this:
image

But, if i click yes and assign the basic Mannequin Skeleton the animations seem to break and the character doesnt move anymore at all.
Also there seem to be two MF_Run_Fwd Sequences in my game, is that cause one is for UE4 and the other for UE5?

Sorry if those questions sound silly but im quite new to all this ^^

thanks in advance!