QT 5.2 app cannot start (Bad allocation error) when Qt5Core.dll is in app directory

I have a funny problem on my machine Windows 7 x64, using QT 5.2 for the GUI

I'm not able to start the app I always receive the error

First I thought I had a broken dll, so through some trial and error I found a solution: I add the QT5Core.dll via enviroment path, and NOT directly to the app folder. Then the programm works. If I copy the dll back to the app Folder, Same problem as before!?!?!?1

I'm really confused, because the error only occurs on my machine? Debugging doesn't really help, In code, the error occures here:

MyApplication::MYApplication(int argc, char** argv, int version)
: QApplication(argc, argv, version)  // <<< this call fails!
{    }

somebody can help me? Why is the location of the qt5core.dll a problem?!?!?

UPDATE

I used the profiling function of depends and found the following behaviour: Failing

GetProcAddress(0x76800000 [c:\windows\syswow64\KERNEL32.DLL], "CreateSymbolicLinkW") called from > "dirone\xxxx.EXE" at address 0x00FF2877 and returned 0x7688CCE9. First chance exception 0xE06D7363 (Microsoft C++ Exception) occurred in "c:\windows\syswow64\KERNELBASE.DLL" at address 0x765CC41F. Exception: "bad allocation"

Working

LoadLibraryW("C:\BuildPackages\QT\plugins\platforms\qwindows.dll") called from "dirtwo\QT5CORE.DLL" at address 0x66AA5154. Loaded "c:\buildpackages\qt\plugins\platforms\QWINDOWS.DLL" at address 0x0F380000. Successfully hooked module.

somehow the path to the qwindows.dll is hardcoded into the dll (there is no environment path to this directory) If I rename the qwindows.dll or delete it, startup failes again.

BUT the qwindows.dll is bundeld with our product. It is in a subdirectory ./platforms/ AND the files are the same (diff returns equal)

Somebody have some clue what I should try next?

Check if you already have some qt related environmental variables. Crashes are usually due to this, remove those envronmental variables first. Check whether you have any other qt installed libraries. it would be better if you can post the cal stacks.