Hi, I wonder if someone could help me out here. A friend of mine has given me a 'Monochrome.ctb' file. Does anyone know how I can get this working. Thanks.

What is working now?
 
Do you know what to do with it?

I just have the file. Unfortunately I have no idea what to do with it. 

How much AutoCAD experience do you have?

I'm not sure why your friend had to give you a Monochrome.ctb plot style file when AutoCAD comes with one to begin with.  Did your friend edit the file to suit his own needs and decide to share it with you?John Connor2011-04-07 19:43:55

Less than a year =)

Why did your friend give you the ctb file?

Sorry, I just saw your edit. The file has different lineweight for different colours. It would make my work so much easier to use it. He got it from an Architectural practise he used to work for. 

I see.  Well, AutoCAD already has a monochrome.ctb file.  Do you want to overwrite it with the one you have from your friend?  Or, do you want to rename your friend's ctb file to something different and keep AutoCAD's original monochrome.ctb file?
 

What operating system are you running?  And is it 32-bit or 64-bit?
Is your version of AutoCAD 32-bit or 64-bit?John Connor2011-04-07 19:57:13

I'm running windows 7 (64bit), and AutoCAD 2011 (64bit). Perhaps it's best not to override the existing file. My friends file is called 'Monochrome2'.

Well at least your friend was smart enough to name his version slightly different.  You need to place this file in the proper folder so AutoCAD can find it.  I believe you will find that it goes here:
 
C:\Program Files\AutoCAD 2011\UserdataCache\Plotters\Plot Styles
 
You have plotted from AutoCAD haven't you?

I found mine here: C:\ProgramData\Autodesk\ACA 2011\enu\Plotters\Plot StylesI've now copied and pasted the file there. No, I haven't. Well I have edited the layout i.e. change paper size etc.

I think we are both wrong.
 
I just took a peek in Options > Files > Printer Support File Path > Plot Style Table Search Path and the path is much different than either one of us imagined.  You might want to do the same.  I would recommend putting your friend's ctb file where AutoCAD is already expecting to "see" it.  When AutoCAD went to 64-bit software they followed Microsoft's recommendations regarding folder structure.  The "old" paths do not appear to be used any more.  Sorry for the confusion.  I should have checked Options in the first place.John Connor2011-04-07 20:22:04

I'll be out in the field for a while so I must bid you goodbye.  I'll check back later.  Maybe someone else will jump in here and answer any further questions you may have.

Ah, thanks anyways John. I think I'll leave this for now, as it's a lot more complicated then I expected. I think I can achieve what I want by simply using the different layers and changing the properties to suit my needs. Again, thanks John.

oh, forget my last post. It was actually done. Just had to click on "show hide lineweight" =) Thanks John.