Polyline lineweight by layer ignored.

Hey guys,
I'm hoping that somebody can help me here with a problem that I'm having tonight with AutoCAD 2006. Basically, I'm using a layer that specifies a lineweight. With that layer selected and "By Layer" selected for the lineweight, every single tool uses that lineweight for this particular layer except for the polyline... for some reason, the polyline is not using any lineweight.
The strange thing is that this started happening at some point in the middle of all my work on this project and if I open a new project, the problem doesn't occur. Does anybody know what might be causing this in the first place .. why my lines whcih are using the layer which has a specific lineweight all use the correct lineweight except polylines. (hope that that makes sense ;)). Maybe there's some property that I changed, though I can't recall.
**Any** help is appreciated!! thanks in advance :)

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I'm DEFINITELY no expert but have you checked your layer window to make sure that everything is in order and when you click on your polyline, do you have the bar that shows all the identifying characteristics of what you've clicked on? If you do, does it show that all is right.
Sometimes, for whatever reason, I'll set up an layer and when I view it in the print file that I have set up, a line or two will not be as heavy as they're supposed to be. I'll click on the line, look up at the bar and see that there is an 15 mm set where "by layer" should be. Go figure,as they say.... I have NOT figured out why I get this sometimes.
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May be your polyline(s) have a width <> 0? Check it with the properties command.
Only a shot into the dark Juergen