Under some circumstances the Visual Studio 2005 process can generate locks on the output assemblies while building your projects. This typically occurs in projects with more than 10 projects in one solution.

The really problem is, that you have to close Visual Studio 2005 to bring it back to work.

To avoid these locking situations in the future ensure that:

1. The class browser view is closed

2. Under all projects debug properties the checkbox "Enable the Visual Studio hosting process" is unchecked.