Blackberry Storm re-locked itself??

Hi, I'm new to this forum please can anyone help me? I have a storm 9500 which was originally on vodafone and i bought it from a friend already un-locked and used my 02 sim with no problems. I then decided to sell it so did a full security wipe but the person i sold it to is trying to use an 02 payg sim card in it and she says it will not connect to the network so can't make calls, sms etc but it works with her brothers vodafone sim card, and her 02 sim card still works in her original phone so her sim can't be faulty. I have searched and can find no answer so any ideas? Can the phone lock itself again after a security wipe? if not what could be the problem?

Many thanks.

Once the phone is unlocked, it can not be relocked. Unless you actually connect it to a computer with the proper special software and basically re-flash it. A wipe will not do it.

Ok Thanks. It has apparently just started working again now.......strange.