Had this error come up when trying to retrieve information from Active Directory for  User record - "System.Runtime.InteropServices.COMException - An operations error occurred".

Turns out that I had to take anonymous access off in IIS for this web site and add

<identity impersonate="true" />

to the web.config file.

The code I was using to access AD through ASP.Net is like this:

Dim entry As New DirectoryEntry(_activeDirectoryConnection)