Okay, I'm still not at my computer and i just can't remember the exact layout of the configurations but if you go to Preferences/Folders in Sonar, there will be file paths for different system folders. You want to make sure the icon folder, and its contents, are still intact...
The problem is, everyone has a different configuration so there is really no correct location I can give you. For example, on my installation, I placed the Cakewalk Contents in a separate partition on my System Drive. But...in Sonar Preferences, I'm pretty sure there is a pointer for the Icons Folder that needs to be pointed to the Icon Folder.
Sorry I can't be more helpful, but I can't remember...and I am away from my computer... I know their is an assignable path for the Pictures Cache, as well, which you can delete, which will force Sonar to create a new folder, in the event it is corrupt....