You get “HTTP Error 500 - Internal server error” while browsing any file under a website or virtual directory whose home directory is a UNC. You will also see in IIS logs, the sc-status sc-substatus sc-win32-status as 500 16 1326.
Unknown user name or password configured for the UNC in IIS Metabase.
This “HTTP Error 500 - Internal server error” error occurs only when you have the website or the virtual directory configured for an UNC and it uses specific user name and password to connect to the UNC (not the logon user credentials).
Give correct username and password for connecting the UNC share on the IIS Manager -> Website or Virtual Directory properties -> Home Directory or Virtual Directory -> Connect As -> Network Directory Security Credentials window. Alternatively you can also set UNCUserName and UNCPassword properties on IIS Metabase for the website or the virtual directory when you have this problem.