Osx will not remember my proxy login / password

Question

I am using my mac book air on my comapny's network ( through Ethernet)
I have, as instructed by the IT guy, keyed into the network settings pane ( system pref -> network -> advanced -> proxy) my user name / password, but this will NEVER be remebered
- if I revisit the same preference pane 5 mins later, the fields are empyty ( though I had cleiked "apply")
- and differents programs ( mail, ..) constantly ask for the proxy login/password
Is there a corrupted preference file or keychain ?
Please help, I am getting mad !

Answer 1

Try this:
Reset User Permissions and ACLs in Lion/Mountain Lion
Boot to the Recovery HD:
Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.
From the Utilities menu select Terminal. At the Terminal prompt enter: resetpassword. Press RETURN. When the window opens select your startup drive where it says "Select the volume containing the user account:" At the bottom of the window you will see, "Reset Home folder permissions and ACLs." Click on the Reset button.