LHC@home

I am running Lubuntu 16.04 LTS 64-bit with boinc version 7.6.31 (installed from ubuntu repository) and virtualbox 5.1.10 installed directly from oracle's site with extension pack. I receive the message virtualbox not installed, maybe I have to somehow point the virtualbox installation to the boinc client?
Please help me out!

From Yetis's checklist

1. 
   
2. 
   
3. 
   
4. Check, if (Intel = VT-X / AMD = AMD-v / VIA = VIA-vt) in your BIOS is switched on. To check you can use a great tool from the web. Download LeoMoon CPU-V and check if it gives you 2 green okays.
   
   
5. Did you try to crunch Projects using VMs in the past while VT-X was not enabled? Could be that BOINC has kept this in mind!
   
   To check and fix this, first exit BOINC and make shure, all BOINC-Tasks have really finished.
   
   In your BOINC_Data-Directory you will find a client_state.xml. Open this with a simple editor and search for:

             [b]<p_vm_extensions_disabled>1</p_vm_extensions_disabled>[/b]

   
   If this is absent or the number is 0 / zero than all is fine. Otherwise change it to 0 / zero <p_vm_extensions_disabled>0</p_vm_extensions_disabled> and safe the file. Be carefull to save it as a real ascii-file
   
   Be carefull that you closed your BOINC-Client succesfull before you change anything in client_state.xml. Otherwise BOINC will overwright your changes

As it seems I have Core 2 Duo E7300 @ 2.66GHz CPU and as per the specifications it does not support Vt-x but that should not be a problem as I was running vLHC@home task on this same PC but 32-bit version of the same OS.
I checked <p_vm_extensions_disabled>1</p_vm_extensions_disabled> in the client_state.xml and it was set to 0.
This issue came up only after changing to 64-bit Lubuntu 16.04