Dimension Pro is my go to synth and it doesn't crash for me.
It is used in almost every project I do.
I've completed almost 2 dozen projects so far using Sonar X2 exclusivley with up to a 8 or more instances just to let you know how much I use it.
It *may* be that certain patches cause problems with Dimension and I just happen to never have found the ones that cause problems.
Which version of Dimension are you using?
If I were in your shoes, I would remove everything related to Dimension Pro, and do a fresh re-install of version 1.5. This is assuming you are not having other problems with Sonar or your DAW.
As far as using Dimension Pro as a Multitimberal instrument there are limitations.
You cannot load 4 different programs into a single instance of Dimension. You can only load 4 instruments or sounds. Some programs take more than 1 bank because they are layered sounds.
I usually do not bother with setting Dimension as Multitiberal and just load a new instance.
I have Dimension Pro and samples located on my system drive.
Have you tried to insert multiple instances of Dim Pro into your project without selecting a program?
Nothing is overclocked on your system, right?
Memory settings are correct?
Memory is on the list of tested memory for your MB?