I ran into a nice little issue in Visual Studio today that I still have no idea why it happened, only that I managed to make it work again.
I had just added a new folder to my project, then a new file (it was a common script for the brail view engine if you are wondering) and went to build my project.
Suddenly the build was failing saying that a conflicting assembly for the task assembly Castle.Tools.CodeGenerator.GenerateMonoRailSiteTreeTask has been found at (full path to VS2005 projectassemblies folder here). The only relavent google result led me to Channel9 which was not overly helpful because it had been working fine.
The GenerateMonoRailSiteTreeTask is loaded via the $(MSBuildExtensionsPath)\Castle.Tools.CodeGenerator\Castle.Tools.CodeGenerator.targets file. I also have a reference to the assembly locally so I thought maybe that was where the confusion was, however even when I completely removed references to the .targets file I still received the error. The assembly was for some reason being copied to c:\documents and settings\chris\local settings\application data\microsoft\visualstudio\8.0\projectassemblies and it was the only one, so something must have made it special no clue what.
Eventually after about 25 minutes of head scratching I deleted all of my *.user, _Resharper.* and *.suo files and tried reopening the project. Thankfully that seemed to fix things so now I can get back to actually getting some work done.