If you’re developing for SharePoint 2010 the Application Pool has a setting called Ping Maximum Response Time with a default value of 90 seconds. In effect, this means that debugging your Web Part, Page, etc. in SharePoint 2010 will only work for 90 seconds and then you get this:
You can increase the value of Ping Maximum Response Time in the Application Pool Settings in IIS:
You can also increase the value for future Application Pools via Set Application Pool Defaults (see Actions menu):
