Microsoft Knowledge Base Article 207671 contains the following summary:
This article provides information about problems with accessing files on a computer other than your Internet Information Server (IIS) server from an Internet Server API (ISAPI) extension, Active Server Pages (ASP) page, or Common Gateway Interface (CGI) application. This article lists some of the issues that are involved and some possible methods to make this work.
Although this article is written primarily in the context of accessing files on network shares, the same concepts apply to named-pipe connections as well. Named pipes are frequently used for SQL Server connections and also for remote procedure call (RPC) and Component Object Model (COM) communications. In particular, if you connect to a SQL Server across the network that is configured to use Microsoft Windows NT Integrated Security, you cannot connect because of the issues that are outlined in this article. RPC and COM may also use other communication mechanisms that have similar network authentication schemes. Therefore, the concepts in this article can apply to a wide variety of network communication mechanisms that may be used from your IIS applications.