Same happened again. Arvixe enabled 32-bit, and came back to me saying the site was working fine (and I had specifically asked them to restart the site and app pool and then test that the site was working). Two minutes later I received notification that the site was down. I could only check it on my phone, but the home page of my site was showing compiler errors (verbose errors had been switched on for the site). I asked Arvixe to revert the change, which they did, and the site came back.
I didn't capture exact details of the compiler errors this time. But I am puzzled how Arvixe could test and say the site was working, only for it to go down moments later with no further changes being made.
I have previously experienced similar compiler errors on the same server after making minor changes in user.config/web.config that were resolved by removing and replacing the /bin folder (to force complete recompilation). The errors I saw that time were like this "Compiler Error Message: CS0433: The type 'ASP.controls_metacontent_ascx' exists in both 'c:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\root\e3cf2397\7b5165fc\App_Web_bci0xhcz.dll' and 'c:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\root\e3cf2397\7b5165fc\App_Web_m4u4hg3p.dll'"
I think my next step is to set up a virtual Server 2012 and test this out for myself, but that will take some time. Any thoughts/advice appreciated.