At my office we have run into some linetype issues. The linetypes would load as flat lines like the SHAPE file is not loading. I tried everything from reloading the linetype to purging and auditing. Nothing would make the linetype stick when the DWG would be reopened. Final solution was to export the drawing to 2000 format and then open the drawing with 2007 and saving. This made the linetypes stick finally. I think the problem was in converting the DWG from 2005 when we installed 2007 and opened the drawing. Its a royal pain, if you run into this issue just convert the drawing to 2000 then open it with your current version of CAD and it should be fixed. Be aware you will lose any AEC objects like points and contours. They get turned into blocks.

:Cheers: