Are you getting this error when you select Registry in the administrator?
The Administrator setting is used only if the attribute clientStorage is not specified in tag cfapplication and the variable clientStorage is not set in the Application.cfc.
Make sure you have client variables set up correctly in cfide and check that they are enabled in your Application.cfc file
Also, you have upgraded to CF 10 from CF 4.5, did you run the code analyzer?
I'd suggest using *anything* but Registry to store client variables, if you in fact need client variables. What OS is ColdFusion running on? If Windows, using Registry can over time bloat and even corrupt the Windows registry, especially if you have a lot of web traffic. If you are on Linux or MacOS, a flat-file registry simulator is used, which is highly inefficient for storing data.
Alternatively, use either cookies (if the amount of data stored in client variables is small and limited to simple values) or use a database.