Cramps in my toes

I converted to Xeroshoes in March. (For the first 2 and a half months I walked 7km each day, finished 2 x 10km races and a half marathon).

I've been living in my Xero's and haven't worn any other shoes since. I bought Vibrams and started running in them last Wednesday.

I occasionally get very bad cramps in my toes after runs or very long walks whether in my Xero's or Vibrams... any advice on that?