Lukas is correct. You should not attempt to upgrade from a previous beta or reuse an existing database when testing out a new beta build. At a minimum you should uninstall all other SolarWinds products since the latest SAM 6.0 beta includes a newer version of Orion core that has not yet been validated against other Orion modules at this time.
If you still encounter issues installing the SAM 6.0 beta after uninstalling other SolarWinds Orion products delete the “C:\ProgramData\Solarwinds\”, “C:\Program Files (x86)\SolarWinds” and “C:\Program Files\SolarWinds” directories, as well as the “HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\SolarWinds” registry key. Then try the installation again.