Unable to delete registry key

Regestry keys, like files, have permissions on them. Right click on the folder for the key you are trying to find out about and see if you can click on permissions.

If you can not even do that there is a hack you can do to run a app as SYSTEM instead of administrator.

Go download PsExec. Open a command prompt as administrator (by right clicking on the command prompt shortcut and clicking run as administrator). Run the following command:

psexec -i -d -s c:\windows\regedit.exe

This will launch regedit with the system account (make sure you do not have any copies open already) and see if you are able to delete those folders.

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P.S. Check to see if solidworks created any users or groups on your machine and delete them (delete the corresponding folder in the C:\Users folder too), I had a similar issue when the user SQLServer installed got corrupted, the only sign was a registry key could not be created/deleted during the setup process.