Virtual Directory Physical Path Credentials for Specific User Getting Bad Data Error as This Portal No Longer Window Authentication

I have this portal that contains applications that range from classic asp to asp.net 4x. The transition from WIA to Forms Authentication has been accomplished manually as this delicate monstrosity will not accept any other way. I have only one hurdle left and this is accessing the virtual directory that stores images and documents for one of the apps and which no longer have the physical path credentials supplied by window authentication.

There is no application to control this virtual directory and I need to transition from Application user(pass-through authentication) to Specific user in IIS 7.0

I have tried to Set Credentials for a generic user and my own admin account but get the Bad Data error 0x80090005 which generally tells me there is no encrypted credentials in applicationHost.config

I assume that the logon type is clear text and these keys should be in the applicationHost.config.

Any hints at how to create these keys would be appreciated.

I ran the command that Lex Li pointed me to:

appcmd set vdir /vdir.name:"ExampleSite/ExamplePathDir" /userName:"username" /password:"XXXXXXXX"

And received the Bad Data error:

ERROR ( hresult:80090005, message:Failed to commit configuration changes. Bad Data.