Did you try using the flag rw?
The kernel module in power kernel should be able to write, but it's not the default since it's still experimental. If you're not specifying rw in the flags it's probably defaulting to ro. If the fs module truly is the read-only one as someone suggested here, using rw will fail to mount, and dmesg should show a kernel message to that affect.

If this is something you can use vfat on (a storage drive, etc) then you should really use that instead. NTFS is great and all, but it's proprietary and thus not well documented or supported in open source code. There are simple command-line drive format tools out there that can format very large drives with vfat without an issue.