Whenever I try to set 'def' bones as parents of the mesh it says: Bone Heat Weighting. Failed to find solution for one or more bones.
Hi kkizilkrallik, this is really frustrating when this happens.
Sometimes it happens when the mesh isn't quite symmetrical (as well as many other random reasons)
Here's some things you can try (in no specific order):
-in edit mode on the mesh, see if you can "snap symmetrical" and then try again
-if it fails of some bones, just track down which bones they are by selecting them and looking at the weight maps
(you will probably need to do some weight clean up anyway so the 'failure' might not be an issue)
-If you want to track down which bones are playing up, you can select one (or more) bones and then apply the automatic weighting manually to check for the error.
Hope that helps.
Sometimes it 'fails' but it's not an issue, so just do some testing on your rig to see. Good luck.