Hi all, what happen to my cache with background synchronization if the server lose accidently the cache? Windows 7 will sync my cache and I will lose all my files?

I don't really understand your question. The cache is stored on the client pc, not on the server. If files are deleted on the server, this will be reflected in the local cache, in that it will be deleted locallly too when synchronization takes place. There is no chance of losing files if they are secure on the server, even if your pc were to crash.

sorry, probably I was not clear. My question was what happen if, for example, i change my server without backing up the files. Is there a way to tell to the server to get the files from the client? or is there a way to resync the client cache with the server?

No, you cannot use the offline files cache as a form of 'backup'. It was not designed for this purpose. Copy the files from the server to a folder on the local hard drive of the pc, or back them up to a removable device, before removing the server.

thanks.