mesh generation path

The first step of my mesh generation is openscad. I create a stl file which is used with netgen. I generate my mesh and save it in gmsh2 format. Then I use gmshToFoam to create my constant/polymesh files. The gmsh2 format step is mandatory in the frame of the simulation. Using checkMesh, I state that all my mesh volumes are negative? Can you give me some advice on the way to avoid it. I join to my question a simple stl file example to reproduce the problem.
Thanks in advance.

PS: Here the verbatim of the checkMesh command:

Checking geometry…
Overall domain bounding box (-0.127 -0.254 -0.01) (0.127 0.254 0.01)
Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
Mesh has 3 solution (non-empty) directions (1 1 1)
Boundary openness (4.20788e-18 -7.6507e-19 1.11891e-16) OK.
***High aspect ratio cells found, Max aspect ratio: 6.64086e+99, number of cells 419
<<Writing 419 cells with high aspect ratio to set highAspectRatioCells
Minimum face area = 6.61942e-05. Maximum face area = 0.00303486. Face area magnitudes OK.
***Zero or negative cell volume detected. Minimum negative volume: -2.18502e-05, Number of negative volume cells: 419
<<Writing 419 zero volume cells to set zeroVolumeCells
Mesh non-orthogonality Max: 179.91 average: 149.656
***Number of non-orthogonality errors: 647.
<<Writing 647 non-orthogonal faces to set nonOrthoFaces
***Error in face pyramids: 1676 faces are incorrectly oriented.
<<Writing 1029 faces with incorrect orientation to set wrongOrientedFaces
Max skewness = 0.594007 OK.
Coupled point location match (average 0) OK.[/i]

Failed 4 mesh checks.[/b][/i]

Attachment: attach.tar.gz