CedricM
I just installed Pentagon 1 with my Sonar X3 setup files to add it to my Platinum installation.
You can choose custom install then only select Pentagon and not even install X3 or anything else.
 
After that:
Open regedit.exe
Go to HKEY_LOCAL_MACHINE\SOFTWARE\rgc:audio
Software\Dxi\Pentagon I
Right click on the Pentagon I folder and select
permissions
Set the permission for group users to allow full access and
click ok

I tried this, and Pentagon is installed but doesn't run. And the promised reg keys don't exist. Can someone export their keys and I can try adding them? 
 
Running as admin didn't help. 
 
Did anyone have any luck with this?

JonD
 
Did you run Sonar as admin?  I believe that's the step that allowed it to work for someone.

Ah, figured it out, I needed to install the 64 bit version instead/as well. Seems to be working now!
(I ran the X3 installer and Sonar Platinum both as admin)
 
Ah, figured it out, I needed to install the 64 bit version instead/as well. Seems to be working now!

I tried all of the above suggestions to get Pentagon to run in Sonar Platinum x64.  I also have Sonar x3 32-bit installed, which runs the DXi version OK, if I start Sonar X3 as administrator.
 
The following steps worked for me with mixed results for Platinum, as there are still some issues.  My system is running Sonar X3 (32-bit) and Sonar Platinum (64-bit).
 
First, I re-ran the X3 installer as "administrator", using the custom installer for X3 64-bit. Unchecked everything except Pentagon and installed only the x64 version of Pentagon.
 
Then I ran Platinum as "Administrator".  Had to do both X3 instrument only install and Platinum "Run as administrator" in order to be able to insert Pentagon DXi without error.
 
Issues:
For some reason in Platinum, Pentagon also shows up under VST2's. Attempting to insert this version crashes Sonar. Avoid.
 
Note: Inserting Pentagon into a new, blank Platinum project works.  Deleting Pentagon from a new saved project with no other VST's inserted works OK.
 
Attempting to insert Pentagon into existing Platinum projects with certain other VST's already assigned (undetermined yet), results in a white Pentagon GUI when the instrument page is opened.  Pentagon plays the default patch OK, but unable to configure synth in this situation.
 
Attempting to delete Pentagon synth causes Sonar Platinum crash, when running as administrator.  Workaround, start Platinum normally, open the saved project while ignoring the missing plugin alert, then delete Pentagon while greyed out in synth rack.  No crash.
 
I guess I can live with using Pentagon in X3 only, but it sure would be nice if this worked a bit smoother in Platinum.  It's still a cool synth.

scook
Yes, appearing as VST is not correct unless it was purchased separately It has been a long time but I believe the retail version shipped DX and VST format 32bit only. The Pentagon bundled with SONAR has always been a DXi. While I have Pentagon installed, it is mostly for testing purposes.
 
If one is willing to edit the registry, it is not necessary to run SONAR as administrator.
 
Users need full control over HKEY_LOCAL_MACHINE\Software\rgc:audio software\DXi\Pentagon I
Make this change to the registry and Pentagon should load without SONAR running as administrator.

Thanks scook!  Registry hack was successfull 

scook
Only paths containing VST2/3 plug-ins should be scanned. Scanning unnecessary paths has been known to cause problems.

OK, pulled that extra path out of the scan. Seems to have cleaned up the duplication, no longer necessary to exclude it.
Thanks!

Is there a setting that will allow me to run everything as the administrator automatically, since I am the only one who ever uses my computers?

Pentagon works for me in SPLAT. However, when I was on windows 7 I had issues and resolved this by moving it to different folders. I can't remember how I got this to work but when I went to SPLAT it just loaded just like any other Dxi. 
 
Also, what you could do is load your old in 8.5 disk and do a modified load of the plugins and just choose which one you want. Direct it to the correct folder if needed. I did this with the Lexicon Pantheon. 
 
Hope this helps. 

CedricM
I just installed Pentagon 1 with my Sonar X3 setup files to add it to my Platinum installation.
You can choose custom install then only select Pentagon and not even install X3 or anything else.
 
After that:
Open regedit.exe
Go to HKEY_LOCAL_MACHINE\SOFTWARE\rgc:audio
Software\Dxi\Pentagon I
Right click on the Pentagon I folder and select
permissions
Set the permission for group users to allow full access and
click ok

Related: I have X3pro online in my account but I'm not seeing Pentagon (my fav). Is it interrogated into the X3 installation?
I know I have it on my old laptop. So I must have got it someplace. ha!
 
peace!
  

Bristol_Jonesey
No I'm pretty sure it was gone in X3, but it was definitely there in 8.5
 
So..... 8.5, X1 or X2 saw it's demise

I have the Pentagon DXi installed in Platinum.
 
The installer is definitely still there in the X3 installer.  I have 8.5, X1, X2, X3, & Platinum.  It's gone in Platinum.
 
I only put X3 and Platinum on my fresh Win 10 after clean installing.
 
Try re-running the X3 installer, select advanced install, and uncheck everything except the Pentagon DXi.  You should be good to go.

abacab

Bristol_Jonesey
No I'm pretty sure it was gone in X3, but it was definitely there in 8.5
 
So..... 8.5, X1 or X2 saw it's demise

I have the Pentagon DXi installed in Platinum.
 
The installer is definitely still there in the X3 installer.  I have 8.5, X1, X2, X3, & Platinum.  It's gone in Platinum.
 
I only put X3 and Platinum on my fresh Win 10 after clean installing.
 
Try re-running the X3 installer, select advanced install, and uncheck everything except the Pentagon DXi.  You should be good to go.

Cool, Thank you both!
Peace