AutoCAD LT lines not visible

[LOUISFUSCO5679]

When I open one particular drawing on computer "A" it contains a layer called "minor contours" and all of the information from that layer is shown in the drawing. When I open the same file on computer "B" all of the minor contours lines are missing. The major contour lines and text are visible but the minor ones are not found. The one layer that contains the minor contours is there and I can draw new informaiton on that layer and it is visible. Also, if I was to save the drawing on computer "B" and re-open it on computer "A" the minor contours are no there. If i was to save the file on computer "A" and re-open the file on computer "A" the contours are there. 

Also, I have tried this on another computer and it reacts the same as computer "A". For some reason it is just computer "B" that is not able to see the files.

So you are aware all of the computers are using autoCAD LT 2013 and are running windows 7. They are also all hp models with almost the same internal hardware and software. 

Does anyone have any idea how to fix this so that computer "B" is able to see these contour lines and save the file without loosing the information.

Thank you

[pendean]

Are these files from Civil3D version of AutoCAD? computer A has the required enabler installed, computer B does not perhaps:

http://usa.autodesk.com/adsk/servlet/ps/dl/index?siteID=123112&id=2334440&linkID=9240818#section1

[LOUISFUSCO5679 · Accepted solution]

Thank you for the information. I installed the enabler on computer "B" and it was able to see the lines. But then when I opened the file on computer "A" the lines were missing. So I installed the enabler on all of the CAD computers and now every computer can see the lines. Thank you for your help Paul Fusco, RLA, ASLA Senior Landscape Designer Louis Fusco, Landscape Architects P.O. Box 362, Pound Ridge, NY 10576 Office (914) 764-9123 Fax (914) 764-4533 pfusco@louisfusco.com www.louisfusco.com