Entry Point Not Found-QtCored4.dll

[ratzz]

I am working on windows 7 with Qt creator 2.4.1 . I have made a sample calculator and it was working fine . one fine morning when i run the same code the code ran to an error .The debugger error is shown below
(12e4.188): Unknown exception - code c0000139 (first chance)
Process crashed
eCDB crashed
dNOTE: ENGINE SPONTANEOUS SHUTDOWN
dState changed BY FORCE from EngineSetupRequested(1) to EngineShutdownOk(22).
dState changed from EngineShutdownOk(22) to DebuggerFinished(23).
dQUEUE: FINISH DEBUGGER
dNOTE: FINISH DEBUGGER
dHANDLE RUNCONTROL FINISHED
sDebugger finished.

When i run the same exe file i got the error message "Entry Point Not Found" (attached below)
I copied the QtCored4.dll found in the C:\QtSDK\Desktop\Qt\4.7.4\msvc2008\bin to the C:\Windows\System32 still same error .. Even copied to the folder where exe is present.

Please suggest me to solve this.

Thanks.