Problem was resolved by manually adding release build directory:
build-myQtConsoleProject-Desktop_Qt_5_1_0_MSVC2010_32bit-Release
From reasons unknown, probably something with permissions, Qt created debug folder such as: C:\Users\Nenad\Qt\opencv2cookbook\build-myQtConsoleProject-Desktop_Qt_5_1_0_MSVC2010_32bit-Debug
but was unable to do so with: C:\Users\Nenad\Qt\opencv2cookbook\build-myQtConsoleProject-Desktop_Qt_5_1_0_MSVC2010_32bit-Release
Noticed it after I clicked on Projects Build Settings. Path for Release was in red indicating that it can't be found.
Later it happened again. By checking project folder I realize it was set as "read only". Setting this folder's permission definitely resolved this issue.