If the solution or project is under source control, it will be checked out automatically during the conversion. Be sure the ...

If the solution or project is under source control, it will be checked out automatically during the conversion.  Be sure the correct Source Control Plug In is active, and no files are exclusively checked out by other users.

If the solution or project is not under source control, please ensure that all files have read/write permissions.

For Office projects, the Upgrade Wizard will modify your project to target the version of Office you have installed.  If you do not want to change the version of Office this project targets, cancel the wizard and clear the "Always upgrade to installed version of Office" option on the "Office Tools" node of the Tools | Options dialog.

Upgrading of Smart Device projects is not currently supported in Visual Studio 2010.