aspnet_regiis always shows its options

Yesterday I used aspnet_regiis in order to encrypt my web.config and my applicatoin run fine. Today I had to restart the server and my application did not run anymore:

System.Configuration.ConfigurationErrorsException: Failed to decrypt using provider 'DataProtectionConfigurationProvider'. 
Error message from the provider: Key not valid for use in specified state. (Exception from HRESULT: 0x8009000B)

So I tried to reconfigure it with the following command:

C:\Windows\Microsoft.net\Framework\v4.0.30319\ASPNET_REGIIS –pef "secureAppSettings" "E:\Program Files\MyProject" -prov DataProtectionConfigurationProvider

It shows its options, as I run it without or wrong parameters I did some test and it always shows them, no matter which parameter/value I pass. I get no errors.
If I run the commands on my local machine, they work.
What's wrong?