well, i said split it up but all i did was to run archive.
the pst file was corrupt. this may be the source of problem but it's beyong my power in this company to change this setting right now.
all email are delivered to pst file, they are not kept in mailbox in exchange server. and this pst file is kept in another server to which user has mapped. so each time a user opens outlook, it retreives the pst file from the server. i've heard that it makes it much more stable if we keep the pst file local. but as i said, i don't have authority to change that here.
so, to archive the corrupt pst file, i created another pst file and imported from the currpt pst file. and it worked. then, i ran archive.
with the corrupt pst file (before importing), it froze outlook when i tried to attach it to outlook.