Missing Face / Hole in the mesh

Hi,

I’ve just started using blender today and I have a problem (hope im in the right section otherwise im sorry)

I imported a head model from zbrush into Blender and there is a face missing, im not quite sure how that happened, there isnt a hole in the model when i check in zbrush and there isnt a hole untill i enter “edit mode” in Blender. The head was made using symmetry but the hole is only on one side which made me even more confused.

I tried to select the edges around it n press “F” to try n fill it but it says “Error, The selected verticles already form a face”

I selected the face and deleted it just to try that but then the hole “jumped” to the face next to it.

I really hope someone has been in this situation and solved it, im just scared that all the work was a waste.
It was my first attempt to make a head model and I really don’t want it to be ruined.

And once again sorry if i posted in the wrong section and thanks for any suggestions that may leade to solving the problem…

I’m not sure. Try selecting everything (A), removing doubles (W > Remove Doubles) and recalculating normals outside (Ctrl + N).