- You only have an Express edition of Visual Studio installed. Express editions are not supported. ReSharper does support VS2005, VS2008, VS2010 and VS2012 Standard and above (like, Professional, Ultimate, etc.).
- The installer checks certain Registry values when looking for installed Visual Studios. Visual Studio might get corrupted and become undetectable by the installer.
- If you have supported Visual Studio editions installed, run "Control Panel | Add/Remove Programs | <Visual Studio> | Repair" action to restore its Registry entries.