Error reading web.config

[David C]

We have an asp.net 3.5 application that is giving us intermittant errors.
The error is "Error reading configuration information from the registry."

The Configuration Error page is highlighting the identity section below.

<authentication mode="Windows" />
<identity impersonate="true"
userName="registry:HKLM\SOFTWARE\LegalApp\identity\ASPNET_SETREG,userName"
password="registry:HKLM\SOFTWARE\LegalApp\identity\ASPNET_SETREG,password"
/>

A short time ago we converted the asp.net app from 2.0 to 3.5 but I don't
think that contributed to this error, but I am not sure. Can someone help?
Thanks.

David