I have a seemingly reproduceable problem with a new 2.1.6 installation.
As I mentioned in a separate post I made some minutes ago I have some tools that require process elevation and the problem I'm having seems to always happen after one of those apps has run.
The sequence of events is this:
1) I use the RUN button to launch a command-line tool called TCC which requires process elevation, so I get the dialog my other post is complaining about.
2) I click OK and TCC runs normally.
3) Back in MO2 I then, say, run LOOT.
4) The console window for usvfs_proxy_x86 opens.
5) An ERROR dialog appears saying "Unhandled USVFS proxy exception (line 110): The system cannot find the file specified."
6) I click OK and LOOT opens normally.
I assume line 110 means something to the programmer who wrote this, sadly I'm not he so I have no idea what it's referring to, also It'd be nice when an error like this occurs if name of the file which is a problem was actually included in the error message, it helps users try to fix problems.
Right now I have zero idea what the problem is or how to proceed, having never seen this with 2.1.5.
I have uploaded the log files I could find from MO2. Note that in one there's a message saying it failed to spawn TCC.EXE, this is bogus, TCC DID run. Because the tools seem to run I'm not sure if this is a real problem or not, but given problems with the VFS could corrupt game save files I'm leery of using MO2 in this state.
As extra information, after the error occurs every attempt to run tools will get the exception dialog, only exiting MO2 and restarting makes them stop, until that is I run another elevated process and the dialog start happening again.