Full memory (La mémoire est saturée)

All, 

I own a S60 and yesterday on my favourite golf course I had the unpleasant message (Full memory - la mémoire est saturée in french) ... I could not do anything anhmore without regular vibration on my wrist ...

I have no idea how to clean it, neither in the watch nor with my mac ...

Could you help please ? I do not understand why I can not find any clue on the web ....

Thanks.

Steve