problem with "rpm -bb" , 1 out of 1 hunk ignored ...error: Bad exit status from /v
 

i want to do some modifies to postfix source.
Below is my steps:
1), i download the src.rpm of postfix ,
2), rpm -ivh postfix.src.rpm
3), cd /usr/src/linux/specs
4), rpm -bp postfix.spec ,
5), cd /usr/src/linux/build/postfix/src, do my modifies to the source code
6), tar and gzip postfix to postfix.tar.gz ,and cp it to /usr/src/linux/sources/ to override the old one.
7), cd /usr/src/linux/specs, and rpm -bb postfix.spec ,

then the error occurs,
it first says :"the next patch would create the file postfix-contrib/README, which already exist !"
no matter i choose 'N' or 'Y' , at last , the error code like that:
1 out of 1 hunk ignored ...error: Bad exit status from /var/tmp/*****

i am puzzled because , even if i don't modify the source code ,

just tar and gzip (tar cvf postfix.tar postfix , gzip postfix.tar )/usr/src/linux/build/postfix to postfix.tar.gz and cp it to override the same one(size is different , more bigger that that one)in /usr/src/linux/sources/ , the same error also exists .

so , what 's the problem ???