OK, looks like my USB drive was NTFS, as when I formatted it to FAT32, it worked fine.
Thought NTFS worked with StickMount, NMI does.
EDIT: Just found the following of the description of the app on GP:
----- Filesystem support -----
The filesystems supported depends on your device firmware. On most devices, at least vfat/fat/fat32 and ext2/3/4 are supported. On the latest Android versions, ntfs is also supported in read-only mode. Some devices also support exfat out the box, but most do not.
StickMount can utilize the "ntfs-3g" and "mount.exfat-fuse" binaries to add support for ntfs (untested) and exfat, but these are not included. If you place the "ntfs-3g" or "mount.exfat-fuse" files in the root of your internal storage ( /sdcard ), StickMount will automatically use them.
You can find the needed files here:
ntfs-3g:
http://forum.xda-developers.com/attachment.php?attachmentid=1145436&stc=1&d=1340293802mount.exfat-fuse:
http://forum.xda-developers.com/attachment.php?attachmentid=806200&d=1323109372