It turned out that the driver installation was not complete. After running the VCP_V1.4.0_Setup.exe another exe should be executed to finish the installation of the driver.
The correct steps:
1- Uninstall previous versions (Start-> Settings-> Control Panel-> Add or remove programs)
2- Run your "VCP_V1.4.0_Setup.exe"
3- Go to Your installation directory - Example, C:\Program Files (x86)\STMicroelectronics\Software\Virtual comport driver
4- Go to Your OS version directory ([Win7] or [Win8])
+ Then :
- Double click on dpinst_x86.exe if you are running a 32-bits OS version
- Double click on dpinst_amd64.exe if you are running a 64-bits OS version
+ Follow the instructions.
These are included in the readme file, which is only attached if you download the driver from the official site.