"There was a problem enabling FileVault." Error Message.

After several attempt trying to enable the filevault on the newly fresh nstalled Mac OS X Mountain Lion, the same error messages appears:

There was a problem enabling FileVault.

Problems were encountered with the disk “Mac HD”. Please turn off FileVault, verify and (if necessary) repair the disk with Disk Utility, and try enabling FileVault again.

Each time I've done the followings:

1. I've turned FileVault off.

2. I've erased all partitioned on my hard disk drive, using the USB disk containing the installation files of Mac OS X Mountain Lion.

3. I've created a single Mac OS X Journaled, non-Encrypted partition using the disk utility and instaled the OS on it.

4. I've followed the initial proccess of the newly installed OS by entering the WiFi credentials, AppleID and password and ...

5. I've restarted the system after first boot.

6. I've just enabled the FileVault after logging in without running any application or plugging any device or even using the system for about 6 hours!

But every time the same error occoured.

My system hardware specifications are as follows:

MacBook 13-inch, Aluminum, Late 2008

Model Identifier: MacBook5,1

Processor: Intel Core 2 Duo 2.4 GHz 3 MB L2 Cache

Memory: 2x4 GB 1333 MHz DDR3

Graphics: NVIDIA GeForce 9400M 256 MB

Misc:

Boot ROM Version: MB51.007D.B03 / SMC Version (system): 1.32f8 / Sudden Motion Sensor State: Enabled

HDD: 500.11 GB TOSHIBA MK5065GSX Revision: GJ003A

Native Command Queuing: Yes / Queue Depth: 32

Removable Media: No / Detachable Drive: No

BSD Name: disk0

Rotational Rate: 5400 / Medium Type: Rotational

Partition Map Type: GPT (GUID Partition Table)

S.M.A.R.T. status: Verified

Volumes:

disk0s1:

Capacity: 209.7 MB (209,715,200 bytes) / BSD Name: disk0s1 / Content: EFI

disk0s2:

Capacity: 499.25 GB (499,248,103,424 bytes) / BSD Name: disk0s2 / Content: Apple_CoreStorage

Recovery HD:

Capacity: 650 MB (650,002,432 bytes) / BSD Name: disk0s3 / Content: Apple_Boot

Please Help!