Hello,
Im very beginner of PyCAM.
The test is: Two cilinders and boolean difference, and boolean union on cube scaled.
Then export to stl and this is the log from PyCAM when import:

09:46 INFO Psyco is not available (performance will probably suffer slightly)
09:46 INFO Disabled parallel processing
09:46 WARNING Failed to locate the fonts directory 'fonts' below ''. Falling back to '/usr/share/librecad/fonts, /usr/share/qcad/fonts'.
09:46 INFO Font directory: /usr/share/qcad/fonts
09:46 INFO Imported STL model: 839 vertices, 0 edges, 1444 triangles
09:46 WARNING Skipping invalid triangle: Point35789<-1.27031,0.587779,0.215795> / Point35790<-1.27031,0.587779,0.108362> / Point35791<-1.27031,-1.41222,0.108362> (maybe the resolution of the model is too high?)
09:46 WARNING *** skipped 7 similar message(s) ***
09:46 WARNING Inconsistent normal/vertices found in facet definition 9 of 'file:///home/j3n4/Documenti/test/test.stl'. Please validate the STL file!
09:46 WARNING Skipping invalid triangle: Point35981<0.312786,0.170874,0.228756> / Point35982<0.312786,0.170874,1.878> / Point35983<0.415338,0.0459141,1.878> (maybe the resolution of the model is too high?)
09:46 WARNING *** skipped 137 similar message(s) ***
09:46 INFO Imported STL model: 209 vertices, 0 edges, 218 triangles

Hi,

the above warnings tell you that the exported model does not seem to be clean (or: PyCAM's importer is not perfect).
Which program did you use as a modeler? OpenSCAD?
Some people recommend meshlab for cleaning mesh models - did you try that?

btw: how does the object look like? Is it completely broken or still looking fine?

cheers,
Lars