Thanks, Timo. Yes it was an Avira issue.
polink.exe was missing from the \bin dir.
Thanks to your hint, I checked Avira's Quarantine list, found polink listed and restored it.
I tried a compile, Avira flagged polink again, I set it to 'Allow' and ran several more compiles.
All seems to be working normally, must have been an Avira update that included new virus footprints that triggered the quarantine.
Thanks again, Timo.