I managed to fix it !

It was apparently a conflict with the USB drivers due to Logitech hardware !!!

Here is the procedure I followed :

Correcting Windows Logitech (or other 3rd party) Driver Conflicts
If you are connecting Pocket POD to a computer running Windows XP or Vista but cannot see any ports in the Ports dialog, there is a possibility that you also have Logitech (or other company’s) webcam,
laser mouse or wireless mouse drivers that are conflicting with the Windows USB MIDI driver.
The problem Logitech driver is called LVUSBSTA.SYS. Here is a procedure to clear out this driver from your
Windows XP system, but bear in mind that it involves editing your registry which requires extreme care.
Psicraft Designs and/or Line 6 will not be responsible if you mess up your windows installation while following
these instructions , so if in doubt have a qualified friend perform these steps!
1. Run Regedit from the Windows Start->Run… Menu.
2. Navigate to the following key:
HKEY LOCAL MACHINE /SYSTEM /CurrentControlset /Control /Class / {6BDD1FC6-810F-
11DO-BEC7-08002BE2092F}
3. Click on this key and delete the "LowerFilters" item.
4. Navigate to the folllowing key:
HKEY LOCAL MACHINE /SYSTEM /CurrentControlset /Control /Class / {6BDD1FC5-810F-
11DO-BEC7-08002BE2092F}
5. Click on this key and delete the "UpperFilters" item.
6. Return to the root of HKEY LOCAL /MACHINE /SYSTEM /CurrentControlset /Control /Class /
7. Launch a search (i.e Ctrl-F with the option to search in "Data") and type "LVUSBSTA". Any time this
is found in the "Control / Class" area of the registry, only delete the "LowerFilters" item (which is
where LVUSBSTA will be found).
Now your class-compliant USB MIDI port driver should be operational.