Encrypt Web.config using aspnet_regiis.exe in ASP.Net

Hi, 

I just read and tried to follow the instructions in the post entitled "Encrypt and Decrypt Connection String in App.Config file". I keep getting the error "Failed to encrypt the section 'connectionStrings' using provider 'RsaProtectedConfigurationProvider'. Error message from the provider: Object already exists."

Although I haver been trying for several days to get this to work, I am even getting the error on app.config files in projects that I have never tried to encrypt.

What am I doing wrong?

Thanks,

Gretchen