can't change mailman site password

when trying to set the site password for mailman i get the following error:

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server:~ admin$ /usr/share/mailman/bin/mmsitepass
New site password:
Again to confirm password:
Traceback (most recent call last):
File "/usr/share/mailman/bin/mmsitepass", line 105, in <module>
main()
File "/usr/share/mailman/bin/mmsitepass", line 96, in main
Utils.set globalpassword(pw1, siteadmin)
File "/BinaryCache/mailman/mailman-132.1~11/Root/usr/share/mailman/Mailman/Utils.py" , line 396, in set globalpassword
IOError: [Errno 13] Permission denied: '/private/var/mailman/data/adm.pw'

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what's wrong?