Dimension Pro is telling me I have 5 days to register the product but the serial number does not match the one in command centre and if I try and register with the serial number it gives me I am told this product belongs to another customer

Do you have previous versions of Sonar? I probably have 5 licenses of Rapture and DP. I don't install them since they are already there. 

When I installed X3, I had this problem; if you run the app which should have installed on your desktop as an administrator, you can enter the reg code there and it will go through.

If you have Dimension already installed, as of a previous Sonar X3 whatnot, then installed new Sonar from Command Center and also select Dimension Pro, this can happen.
The solution is to uninstall Dimension Pro then run the current one from Command Center again.
 
This is what I had to do, because I had the same problem as being mentioned from the OP. 

Thanks all will give a try.

SimpleManZ
The solution is to uninstall Dimension Pro then run the current one from Command Center again.

That's right...but this way you can't choose the install path....and Dimension Pro will be installed by Command Center in the default path C:\program files\cakewalk.....with over 3,5 gb of data (plus expansions).... I've asked in another thread if is possible to set a new path for all applications (NON default C:\program files\Cakewalk...) or force Command Center to scan applications previously installed in NON default paths.
Command Center was designed to help customers installations so I figure out that everything is demanded to the software with the aim NOT to generate confusion.
 
This path customization should be addressed (with a deep search scan inside registry for installed software) and included in one new advanced option tab of Command Center itself for advanced users only.
 
At time of writing you can set download and VST directory in the Command Center options but no applications path customization is available (i.e. Rapture and Dimension Pro).
If you try to install them manually, in NON default path, Command Center will not scan them and, as a result, they will be flagged with a red dot (as uninstalled).
They are full functional but no fixes or updates will be auto searched for red marked software....

Hmmm. So if one wanted to use an existing DimPro installer (I have one marked 1.5 with a file datestamp of 2013) rather than downloading it again through the CCC, and one were to use the new serial provided with Platinum (and showing in the CCC), and let it install in the usual place, will CCC then scan it and find it and make it updateable? Or is the only way to get something to register in the CCC to let it download a whole new copy?

Well that now explains why its not seeing my previously installed version of Melodyne Editor edition.