Before replying consider that:
1-I’ve googled this many many times but still auto rigging fails.
2-Take a look at the blend file before replying
Error: Bone heat weighting failed to find solutions for one or more bones (or something like that)
Present.blend (7.92 MB)
Two errors
1 - Separate the teeth to their own object before applying weights. You can join them back afterwards and just weight paint them
2 - Always take time to check your mesh for errors.
In edit mode use the Select / Non Manifold in vertex select. This will highlight the areas where your mesh has holes. Merge vertices (Alt+M) to close these holes
After doing both of these things I get no automatic weight errors
EDIT. Also please use the support forums in the future for support questions. Blender Discussion forum is NOT for support questions. Thread moved.
Thank you very much, it is hard to find answers these times 
Can i ask one more thing, when I assign automatic weights, it does it without errors but the shoulders twist
Well you’ll have to go and fix these manually. Auto weights just gets you 10% there, the last 90% is down to you
