Assembly error!!!!

hi every one. Today while doing assembly I just rename some parts in catia and I saved that file. But when I reopened the assembly file some parts ( which I renamed in catia during assembly) got missing and some window was coming showing some error. But I don't understand why it happening??? Can any one help me out in this????
Suppose I made one catia model and saved it in desktop as "aaaa". and if while doing assembly if I renamed the same part as "bbbb" and saved the assembly file. and if I reopened the assembly file part which I renamed is not showing.. I hope you all understood this. pls help me out in this.
thanks in advance