Sorry about the delay replying, was out last night. Head is still hurting, so bear with me...
Ok, as I was saying, you need to check that the drive is mapped properly. If you start, run cmd, this will bring up a DOS session. From here type in "net use" (no quotes) and press enter/return. This should list all your mapped drives. The readyNas ones should show up as b: and m: and say OK to the left of them. If it doesn't, e.g. It says "disconnected" then windows can't find the NAS.
Make sure that your local network is marked as "Trusted" on your PC/laptop's firewall software - how you do this depends on the software you use. If it's not, you have to do some awkward config changes.
Move your backup drive mapping from B to a drive letter higher than any local drive on your pc/laptop. Two reasons, the B drive used to be reserved for the second floppy drive, and this can cause problems at times. Secondly, a drive letter before the last local drive can be misinterpreted as a local drive, also causing problems.
Let me know how you get on.