The RSA key container could not be opened

If you still have access to the older machine, you could always decrypt the configuration section on that machine, then copy the unencrypted config file to the new machine (and, if necessary, re-encrypt the file on the old machine).

On Windows 7, the account under which your IIS application pools run by default will likely be ApplicationPoolIdentity (as opposed to ASPNET). To grant permissions, try this:

aspnet_regiis -pa RSAProviderName "IIS APPPOOL\DefaultAppPool" -full

By the way, if you do decide to persevere with copying the key from the old machine to the new one, you should make sure that, when exporting, you export the private key data too:

aspnet_regiis -px RSAProviderName C:\RSA_configkey.xml -pri

And, optionally, to make the key data exportable during the import:

aspnet_regiis -pi RSAProviderName C:\RSA_configkey.xml -exp

I was facing the same issue, But running the commandprompt/powershell using administrator resolved the issue.