Finally resolved......

As usual, pretty simple solution. Turns out it was some kind of errant trace - even though I had thought I disabled the default trace with sp_configure.....

instead of using...

ok - I can't see any application services that would need to be connecting to SQL server..... I'm stumped.

Thanks - I'll check it....

I'm trying to restore the master db - which I thought had to be done in single user mode?