little Hole during HD Geometry

[system]

hi there
im modeling in HD Mode with ~100M Polygons and a small hole appeard, my problem is when i click on close holes i cant go back to HD mode to finish my work
so my question is how can i close the hole and after that going back to hd geometry mode without loosing detail (model is nearly finished)

ok now lines appear also often so i have to go back and load quicksaves but this dont really helps cause next time it apperas somewhere else
I really need help im going crazy im close to finish the model but now all this bugs happen

Kind Regards Laslo

made 2 pictures of the problem:

Attachments

[system]

ok i have also some other questions for the hd workflow
what polycount your model have when u start hd geometry?
how do u get a clean model to start hd geometry on?
any other tips to prevent theseholes and lines in the mesh
could it maybe happen because my pc is to weak so he dont get all information?

PC:
AMD Phenom IIX4 920 Processor 2.80 GHz
RAM: 8GB

Regards Laslo

[system]

it seems to be a rare problem if there is no solution for this problem with keeping all the detail please tell me that ill start from 0 again than