I have a Silverlight client, with a PollingDuplex service client, which works fine under IIS7 - callback messages are received clientside without any problems. However, the same client and service fails on IIS5.1, with the server error The IOutputChannel timed out. It's clear that on 5.1, the server can't call the client back - but why?
Both tests in IIS7 and IIS5.1 are run entirely on the local machine (ie. both client and server are local) - there are no firewalls getting in the way.
Ideas appreciated.