Config Error Failed to decrypt attribute 'password'

I fixed this by disabling Anonymous Access in the application, then re-enabling it immediately. No IIS restart necessary.

I resolved the issue. The problem was C:\Windows\System32\inetsrv\config\applicationHost.config file. In the config file, I deleted username and password definitions for applications and it worked well.

I had the same issue after clone a Web Server.

Solution:

Source Server:

aspnet_regiis -px "iisConfigurationKey" "C:\temp\iisConfigurationKey.xml" -pri 
aspnet_regiis -px "iisWasKey" "C:\temp\iisWasKey.xml" -pri 

Destination Server:

aspnet_regiis -pi "iisConfigurationKey" "C:\temp\iisConfigurationKey.xml" 
aspnet_regiis -pi "iisWasKey" "C:\temp\iisWasKey.xml"

And, at the final, copy applicationhost.config from the source server to destination server.