cifsd expetcts that the 9fs $foo command mounts the filesystem to
/n/$foo where $foo is derived from the smb share name by turning all
upper case characters to lower case.

so if 9fs vac.1 mounts to /n/1 instead of /n/vac.1 you will get a
empty directory in cifsd because it will look in /n/vac.1.

but this does not explain the error 64...

do you logon to the cifsd server with the right plan9 user name?  have
you tried running the 9fs command as the same user?

do you see anything in /sys/log/cifsd?

--
cinap