I'm using Map 3D 2007. I never had this problem with 2004. It's suddenly just happened. Admittedly I had a Lisp script that plotted these automatically for me, to file, direct to a plotter or direct to PDF. It could also handle the two formats I need.
With the update the script didn't work anymore. BUT I've got the script working again (took out old "command" calls and replaced them with VL stuff) but the layouts that I've modified with the script don't plot properly anymore!? They don't even Plot correctly when I setup everything by hand.
What's really strange is....I copied modelspace into a new File....set up a couple of new layouts (exactly the same setups for plotting and Layouts and the same Plotstyle file from the same directory). I then tried to print directly to plotter and then to file (which I sent to the plotter). All Plots were perfect. Seems I've got a bug in the original File (or layouts). ALSO...When I run my script on the new file it crashed at a code call where there is absolutely nothing wrong! I Swear! (It didn't break at that point when I ran it on the original file). It's getting weird.
I'm not sure I understand your Question "All you Objects are set to "By Layer" for Lineweight & "Plot Style"?.
I've checked the .ctb file. All Colours are set to the correct lineweights, i.e. they have different lineweights. It just doesn't print that way (they are all the same weight and very thin - useless)!
I print in colour. I don't know what a stb file is.