Thanks so much for your swift help.
My registry setting for ContentDir was not correct. I have updated this and all now works fine.
I have set up Cakewalk projects on drive D and content on drive C so the things I checked were as follows:
Checked the registry entries using regedit
Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Cakewalk Music Software
ContentDir = "C:\Cakewalk Content"
ProjectDir= "D:\Cakewalk Projects"
Also Sonar - preferences - File - folder locations "Project Files" = D:\Cakewalk Projects
Sonar preferences - Audio data
Global Audio folder "D:\Cakewalk Projects\Audio Data"
Picture folder "D:\Cakewalk Projects\Picture Cache"
Checked the link in "D: Cakewalk projects"
"All SONAR sample content & Tutorials.lnk" points at "C:Cakewalk Content"
Many thanks