All of the Cakewalk sfz engine synths including DimPro and SI have registry entries which govern where the plug-ins find their data. There are usually two keys used by each plug-in:
"Content Folder" - this tell the plug-in where all the supporting files are located
and
"Multisamples Folder" - if this key exists, the path in it is appended with \Mutlisamples and the plug-in looks for samples and sfz in the location. It overrides the Content folder.
1) Unless you want to go a series of SONAR uninstall and reinstall process, manually deleting unreachable installations is the easiest way. Unreachable installations are the ones not referenced by the registry and dlls not in the scan path. Make sure the "good" location has everything by inspecting the Content and Multisamples folders. If older versions had extra expansion packs added, that data will need to be copied OR the packs reinstalled. Alternately the registry could be changed to point to the old location or directory junctions could be used instead of modifying the registry.
2) Look in the registry.
This thread
http://forum.cakewalk.com/FindPost/2673527 contains registry information you may find useful
OR
Uninstall everything, clean up the machine. Install the new version of SONAR and add back old plug-ins from previous installations.