I uninstalled at least two versions of Dim Pro and reinstalled version 1.5. I could see the X64 dll in the VST folder, but Sonar could find only an old version 1.2. Plus, it treated the 1.2 as a new installation that had to be registered,except none of my serial numbers and registration keys worked. I still have X2 installed, so -- just trying random things -- I launched it and was able to register the v.1.2. Later when I was in X3, Dim Pro x64 v.1.5 was available. I have no idea what happened.

This problem popped up while I was in the middle of something else, and I started trying to "fix" it without keeping track of what I was doing. So I got it working, but I'm not much use to you, because I don't know what actually worked.

Best of luck with this and if it's not too much trouble maybe you could let me know the solution, whenever you find it.

I'm wondering if Dim Pro x64 v.1.5 will work in X3 and not X2 due so some interface updates in X3. So Dim Pro x64 worked in X2 or was it x3? Also, I followed up with support to see if they have any status.
 
My real pain point is Protues VX not displaying in X2; works fine as stand-alone - I'll be starting a separate post on that issue. I've read both Proteus VX plugin works in X1 & Dim Pro Installation Problem...and Proteus VX Libraries won't install, but not fully resolving my issue; no install issues and runs fine in stand-along, but display issues with X2. Again, I think the X2 in x64 doesn't play well with others. 
 

musiccontinuum
I'm wondering if Dim Pro x64 v.1.5 will work in X3 and not X2 due so some interface updates in X3. So Dim Pro x64 worked in X2 or was it x3? Also, I followed up with support to see if they have any status.
 
My real pain point is Protues VX not displaying in X2; works fine as stand-alone - I'll be starting a separate post on that issue. I've read both Proteus VX plugin works in X1 & Dim Pro Installation Problem...and Proteus VX Libraries won't install, but not fully resolving my issue; no install issues and runs fine in stand-along, but display issues with X2. Again, I think the X2 in x64 doesn't play well with others. 
 

Weirdly, once I registered my "new" installation of Dim Pro x32 v.1.2 in X2, Dim Pro x64 v. 1.5 began working in both X2 and X3. Prior to that, Dim Pro x64 v. 1.5 was installed in the default location and the standalone worked, but Sonar could not see the plugin. Good luck with Proteus. I don't have that.

Larry - I might try installing the v.1.2 and then installing v.1.5 x64 version and see if that works. I know that EZDrummer requires you to install the x32 patch in order to apply the x64 patch (not sure the logic on that one, unless x64 version is utilizing some of the dll's within x32).
 
 

Latest update, I upgraded to Sonar X3 (Pro), uninstalled Dim Pro x32, installed Dim Pro x64 and it's working.