If you get a http error 500 when previewing a local xpage in a web browser but it works ok in the client here is one solution.

If you run the lotus designer as windows nt administrator then that should cure it.

Another thing to bear in mind is the names.nsf that you reference will be your local personal nab not the server names.nsf.

Enabling the Error display in the xpages database properties page will help with that one.