1) the cable MUST be twisted pair.
2) both ends MUST be terminated with a correct termination ckt.
3) did you read 10 ways to bulletproogh RS-485 found through "Best Serial Comm Appnote site" in links <---
4) both ends must have ground (stable and spinking) within the max common mode rejection specified for the RS-485 transciever you are using.
5) I have never seen the difference shielded or unshielded, but I do shield the twisted pair anyhow.

My problem is that the unit works fine on table with approx.1 mtr. cable.
But it stops communicating with 10 mtr. cable.
would typically be due to 2)

Erik