This application failed to start because it could not find or load the Qt platform plugin "windows" in "".

[allenck]

After using the maintenance tool to download QT version 5.6 in addition to version 5.7 I started getting the error that it could not find the Qt platform "Windows". Before this, I was able to compile and run under 5.7 without this error but now it occurs there as well.

Figuring something was wrong with the Qt installation, I completely uninstalled all instances of Qt and reinstalled 5.6 and 5.7. Same problem.

After researching the problem, I tried adding the define for QT_PLUGIN_PATH to the projects defines. This solved the problem of loading the platform "windows" plugin but now complained: "Could not find QtWebEngineProcess.exe". I added another define QTWEBENGINEPROCESS_PATH and was able to start the app. However, the QWebEngine widget doesn't display anything. However a series of debug messages may explain why:
Qt WebEngine ICU data not found at C:/Projects/mapper_QT/mapper/mapper_app/debug. Trying fallback directory... The application MAY NOT work.
Installed Qt WebEngine locales directory not found at location C:/Projects/mapper_QT/mapper/mapper_app/debug/translations\qtwebengine_locales. Trying application directory...
Qt WebEngine locales directory not found at location C:/Projects/mapper_QT/mapper/mapper_app/debug\qtwebengine_locales. Trying fallback directory... Translations MAY NOT not be correct.
Qt WebEngine resources not found at C:/Projects/mapper_QT/mapper/mapper_app/debug/resources. Trying parent directory...
Qt WebEngine resources not found at C:/Projects/mapper_QT/mapper/mapper_app/debug. Trying application directory...
Qt WebEngine resources not found at C:/Projects/mapper_QT/mapper/mapper_app/debug. Trying fallback directory... The application MAY NOT work.

The same source compiled on another PC with5.6 works fine. My conclusion is that there is something wrong with my QT installation; probably related to qtcreator.conf files.

I might point out that in both cases, I am running under Windows 7 and using the MSVC2013 distribution. I have not recompiled any part of QT except the SQLite plugin.

The version of QtCreator that was downloaded is 4.0.3. However the same problem occurs with an older copy of QtCreator (3.0.1) that I had on my machine

Should I delete all the QtCreator.conf files or is there something in the registry that is causing QtCreator to not work properly?

[raven-worx]

@allenck
this question has been asked a million times already. please use the search.

[allenck]

@raven-worx Perhaps you could provide a link to the solution. I have found numerous posts on this subject however none of them come close to providing a solution. For one thing, most of them are about trying to **deploy **an application. That is not the case here. I am trying to run an application in QtCreator compiled on a clean download of QT. Furthermore, I had no problems until I used the QT maintenance tool to add Qt5.6 to an already existing download of QT5.7. The real question is how can I download a copy of QT that is usable.

[mrjj]

@allenck
Hi
That sounds very strange. (since its in creator)
You could try the offline installer for vs2013
https://www.qt.io/download-open-source/#section-2
Qt 5.7.0 for Windows 64-bit (VS 2013, 904 MB) (info)
Qt 5.7.0 for Windows 32-bit (VS 2013, 909 MB) (info)
OR
Qt 5.6.1-1 for Windows 64-bit (VS 2013, 829 MB) (info)
Qt 5.6.1-1 for Windows 32-bit (VS 2013, 833 MB) (info)
Maybe install to new folder c:\myQt

I have only had such issues once and it turn out to be Avast virus scanner that
silently ate some files :)

I agree that something is funky with your installation. Im not aware of any registry items
that would make it fail like that.
If you make plain new GUI app, can it work?
Its just QWebEngine project that gives errors?

[allenck]

thanks. I found a file called qt.conf in my debug directory. I deleted it and now everything is OK. I vaguely recall downloading such a file when following another post. Anyway it seems to have been the problem so I guess the issue is solved.

[mrjj]

@allenck
ahh, yes that would do it.
It can tell Qt to look from plugins in other places.
http://doc.qt.io/qt-5/qt-conf.html

Good catch :)