When we recently upgraded our project from VS 2008 to VS 2010 everything went just fine. The project was converted and the conversion log didn't report any errors. Two days ago we deployed our web application to the production servers, that's when the problems started to show up.
The application couldn't connect to several services. The error was that the Web Reference URL to the services had been changed from https to http. We hadn’t caught this error in our test environment because the https restriction was not there in that environment.
So if you have converted a project from Visual Studio 2008 to Visual Studio 2010 and you have any web service references that goes to a https endpoint, be sure to check that it hasn’t been changed to https.
I have filed a bug report to the Visual Studio team at Microsoft, so if you get the same problem go there and vote it up, then maybe we can get a solution to it sooner then later.