Error during installation - qmake.exe -query is not parseable

Dialog pops up during installation of Qt Windows OpenSource 1.6.0 x86 online.exe:

Operation 'QtPatch' with arguments: 'windows; Z:\Qt/5.2.1/msvc2012; qt5' failed: The output of
Z:\Qt\5.2.1\msvc2012\bin\qmake.exe -query
is not parseable. Please file a bugreport with this dialog https://bugreports.qt-project.org.
output: ""
created warning message box installationErrorWithRetry: 'Installer Error', Error during installation process (qt.521.win32_msvc2012.essentials):
The output of
Z:\Qt\5.2.1\msvc2012\bin\qmake.exe -query
is not parseable. Please file a bugreport with this dialog https://bugreports.qt-project.org.
output: ""
perform qt.521.win32_msvc2012.essentials operation: QtPatch

• arguments: windows, Z:\Qt/5.2.1/msvc2012, qt5
  Cannot get any query output from qmake.
  Done

It errors several times all in mscv2012 (both 32 and 64) then goes on to complete everything else.

I know that a similar issue QTBUG-32686, but in that case it was a out-of space issue, which I don't have.

I'm installing to a 2TB drive (z that is mostly empty, and I have over 800mb above what the installer needs on the c:\ (and does have 846MB free at the time of the errors). The C: was short at the start of the install, but was increased when prompted by the installer before things where installed.

I had a prev install of QT which I uninstalled, and then (when prompted) deleted the remaining directory . New install is to the same place.