Quote Originally Posted by djprinter View Post
Simplify 3d supports don't stick directly to the build plate very well. To work around this problem I usually put a one layer thin object under all supports that touch the plate.

This is one of the most talked about problems on the S3d website, so hopefully they'll fix it one day.
If you have a part where all your supports bottom out on the bed there is a selection in the support section of S3D where you can set your bottom separation layers to 0 and they will bond much better.