I have a Block Attributes in a drawing that was recieved from the client, then i made some changes in it (attributes) my question is when i try to update it using  ATTSYNC command the whole block attibutes vanishing or disappear...any solution with this?

This happens to me sometimes, and when it does happen, I just UNDO immediately after running ATTSYNC. This usually fixes the problem.
 
Have you tried running an AUDIT on the drawing to check for errors? Also AUDIT any xrefs that may be attached.

i try to audit and i found zero errors, i was wondering how they did this (client) when im creating attributes in my own  i didnt experience this....yes, undo will work  but i need some changes in the drawing