Install as follows:
1) Please make sure that you have the latest version of ActiveSMS installed
2) Download patch from:
http://www.intellisoftwa.../ActiveSMS5.0_Patch8.zip 
3) Close 'ActiveSMS Console' and 'ActiveSMS Test' if running.
4) Goto 'Start Menu->Settings->Control Panel->Administrative Tools', double-click on 'Services'.
5) Double-click on 'ActiveSMSServer', and click 'Stop'
6) Double-click on 'ActiveSMS Email Gateway', and click 'Stop'
7) Extract ActiveSMSServer.exe to C:\Program Files\IntelliSoftware\ActiveSMS (this should overwrite an existing file)
8) Extract ActiveSMSEmail.exe to C:\Program Files\IntelliSoftware\ActiveSMS (this should overwrite an existing file)
9) Open 'ActiveSMS Console' and re-start ActiveSMS.
10) In the 'ActiveSMS Console', click the Email tab.