mount ntfs (windows) file system in /etc/fstab fails at boot

[Kevin Smith]

I am able to mount my windows partition manually by either:

 > mount -t ntfs /dev/ad0s1 /windows

or by putting an entry in by /dev/fstab that looks like:

/dev/ad0s1             /windows          ntfs     ro              2       2

and using command:

 > mount /windows

-however,

If I leave this entry in my /etc/fstab, the OS reports inconsistency 
errors on bootup when it tries to mount and goes into single-user mode.  
I then had to remount / for read-write and delete the line in the fstab 
before it would boot again.

Am I using the wrong syntax for the fstab entry  ?- also, why does it 
mount manually with no error - but complain at boot time ?

-K