Paypal its business model involves freezing accounts for frivolous reasons. Once your account is locked you can not touch your money, but new funds can still enter your account. Nothing can go out. There area great many ways to gets your account frozen. For example: using a different IP than normal, withdrawing a high amount of your funds, paying or receiving from someone who has been flagged, etc.
All this can happen to anyone. From completely innocent charities to political parties or even wikileaks.
Read this:
http://techcrunch.com/2011/12/06/paypal-account-freeze/
Once your account is frozen for such frivolous reasons you then have to jump through a great many hoops through Paypals special frozen accounts support system, which is obviously designed to drive you into despair and make you give up.
I have been through this twice. The last time it took me 3 months and my lawyer getting involved before they released my account.