Edit:
Some people started to mark my question as a duplicate. Do not forget that many similar questions existed when I asked this one (see e.g. the list below). However, none of these answers solved my problem. After a long search I found a comment which had been ignored by all users pointing to the missing lib. Now, many months later, the comment has been changed to an answer. However, when I answered this question by msyself I intended to help other people by directly providing the solution. This should not be forgotten and so far my answer helped a lot of people. Therefore my question is definitely not a duplicate. By the way: The accepted answer within the provided link on top does not solve the problem!
Yes, i used the search:
Failed to load platform plugin "windows". Available platforms are : Error
Deploying Qt C++ Application from Visual Studio qwindows.dll error
failed to load platform plugin "windows" Available platforms are: windows, minimal
However, in my case the problem still persists. I am using Qt 5.1.1 with Visual Studio 2012 and developed my Application on Windows 7 with Qt Creator 2.8.1. Application is compiled in "Release"-mode and can be executed if directly started with Qt Creator.
However, when starting from the "release"-Folder, i get the following message:
This application failed to start because it could not find or load the
Qt platform plugin "windows". Available platform plugins are:
minimal, offscreen, windows.
Folder structure looks like this:
release
+ gui.exe
+ icudt51.dll
+ icuin51.dll
+ icuuc51.dll
+ libGLESv2.dll
+ Qt5Core.dll
+ Qt5Gui.dll
+ Qt5Widgets.dll
+ platforms
Platforms is the folder directly copied from Qt\Qt5.1.1\5.1.1\msvc2012\plugins\platforms including e.g. qwindows.dll. Does not matter if I rename it to "platform" as some other users did. Qt is still not finding the "platform plugin windows", where is my mistake?
Best Answer
Okay, as posted here https://stackoverflow.com/a/17271172/1458552 without much attention by other users:
The libEGL.dll was missing! Even though this has not been reported when trying to start the application (all other *.dlls such as Qt5Gui.dll had been reported).