1. Start -> Run -> regedit
2. Registry Key for server role (HKLM/Software/Microsoft/Shared Tools/Web Server Extensions/12.0/WSS/ServerRole) has to be changed from SingleServer to Application.
NOTE: Please make sure you make a backup of the registry before you make any changes. Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system.