Dimension Pro dll not found by sonar x3

That would bring in the 32-bit Dim Pro.
 
You only need to specify C:\Program Files\Cakewalk\Vstplugins in the search path for VST instruments in the Cakewalk Plugin Manager, and that path should have been added automatically in the Sonar install.  Sonar will detect any sub-folders, so there is no need to specify the entire path to Dimension Pro.
 
Open a Windows File Explorer window, and navigate to C:\Program Files\Cakewalk\Vstplugins\Dimension Pro.  You should see 2 files there - the Dim Pro dll, and the Dim Pro stand-alone program.  If these 2 files are there, and you have the path specified properly, and you have done the installation with explicitly using Run As Administrator (not just logging on with an Admin account), and you have completed the Dim Pro registration process, then there is no reason why Sonar should not find the Dim Pro 64-bit dll.
 
I would think one of the above-listed steps was not completed.
 
What happens if you double-click on the stand-alone 64-bit Dim Pro, from the above folder?  Does it run properly?  Does it want a registration code?  (If it does want a registration code, exit and run again, using Run As Admin, and then enter the registration code).
 
Perhaps for some reason the 64-bit Dim Pro was excluded by Sonar, which you can check in the plugin manager by clicking on the Show Excluded Plugins option.
 
Or, perhaps your download and/or install of Dim Pro was done while antivirus software was running, as that can sometimes cause installation or execution problems.  If so, navigate back to the Cakewalk Store, then temporarily suspend your antivirus software, download Dim Pro again, and install it again, all while the antivirus software is suspended.  You can resume your antivirus software after the install completes.  After registration is completed, by running Dim Pro in stand-alone mode with Run As Administrator, check your search paths again in Sonar, to make sure they are correct, then BOTH Reset AND Rescan your plugins.
 
Lastly, I would not recommend adding 32-bit plugins into 64-bit Sonar, particularly when you have 64-bit versions of the Cakewalk instruments and effects.
 
Hope something in the above helps, 
 
Bob Bone
 
Does