I read some other threads discussing this same problem, but didn't see that anyone had ever solved it (though there was some informed speculation as to the cause).
 
I've created and ACT controller surface and successfully linked the desired controls on my hardware controller. ACT will now successfully follow context and I can use my hardware controller to  control Sonar's console or any plugin I have focused. However, I cannot successfully use ACT learn to remap plugin parameters to my choice of ACT cells (and therefore hardware controls) of most Native Instruments plugins as well as from some other vendors (notably Addictive Drums 2). I follow this procedure as described in the manual and elsewhere.
 
1. Click ACT Learn button on either ACT controller surface or plugin window. Button turns blue.
2. Move parameter(s) on plugin GUI that I wish to remap.
3. Move hardware control(s) that I wish to remap to.
4. Click ACT learn button again. Button returns to gray.
5. Sonar displays dialog " x parameters and x controls were touched. Do you wish to keep these assignments?"
6. Click "Yes"
7. Nothing happens.  ACT control surface still displays same parameter name,  hardware control still mapped to same parameter.
 
When I follow the above procedure with various Sonar included plugins it works exactly as described, the new parameter name is displayed and the hardware control is now mapped to it. It also works with some 3rd party plugins (Image-Line's Sytrus and Gross Beat, for example). 
 
Anyway, just wondering if anyone has been able to get this ACT function to work with NI and other 3rd party plugins. For now, I'm just creating assignable controls in the synth rack for controls I want quick access to which are not mapped by default in the ACT controller, then switching off ACT when I want to use them.

Check my site (see the signature). In particular:
http://www.azslow.com/index.php/topic,5.0.html
http://www.azslow.com/index.php/topic,13.msg107.html#msg107
 
I guess you hit at least VST3 bug (ACT mapping is broken for VST3), may be XML corruption bug as well. I can recommend ACTEditor from MarKo. Note that once some mapping is working, it will work all the time (till you try to "ACT Learn" again). So either Manual editing or ACTEditor mapping, that is one time operation per plug-in (not project specific!).

Thanks for the reply and info. I don't have time to dig too deeply into this today, but I downloaded and installed the files and took a quick look. Just to clarify, AZ controller is a control surface I would load instead of ACT controller surface? And the Sonar ACT editor is used to map parameters to AZ controller?
 
Thanks,
Robert

Not really... For ACT Editor way, you need this tool: http://www.azslow.com/index.php/topic,251.0.html
AZ Controller "helps" to use it if you want, but that is not a requirement. If you want, add AZ Controller to Control Surfaces with Input and Output set to "None" (that is important if you continue to use "ACT MIDI" plug-in). Open AZ Controller property page, ACT Editor will find it then and show the parameter you touch in the VST interface. Without that addition, you will be forced select plug-ins/parameters manually yourself, based on names (and that is not easy for some VSTs).
 
It is important to backup and remove related XML files (better ALL xml files) in that folder, with Sonar closed. That way you will start from ground. Open Sonar, "visit" (just open) plug-ins you want to configure and then restart Sonar. Start ACT Editor, you should see all that plug-ins and default mapping for them. Modify as you like (based on the number of controls you have), close Sonar, save the result in the Editor (in that order). Do NOT use "ACT Learn" during that process.
 
If everything works (there are some situations when that still can fail...), you should get correct ACT mapping. Backup it. From that moment, the mapping should work with any plug-in. ACT MIDI, Generic Surface, AZ Controller, etc.
 
That text can sound as a complicated rocket science till you follow the procedure with 1-2 plug-ins.
In reality that is the only way to get the mapping ready rather quick (less then a minute per plug-in, once you used to it). Alternatives are manual editing XML files (bulletproof but slow) or "ACT Learning" with either surface or ACT section in AZ Controller while keeping an eye on resulting (the second, not used in ACT Editor) file (does not work for VST3). Or give up ACT, which most users do... Your choice