directory Operation not permitted

[J. W. Ballantine]

Hi,

I'm running FreeBSD5-stable and there is a directory named
 "empty" in the /var/tmp/temproot/var path, created by mergemaster,
 that will not allow me , as su, to chmod or remove.  Any time I try
 I get Operation Not Permitted.

There doesn't seem to be anything special about it, any thoughts as to
what is going on with this beast???

When I rerun mergemaster and reply yes to the final should I delete the dir. 
path,
it is removed.

Thanks

Jim