One "gotcha" that I had on my Initial IR to Cranfield was being given a Direct To the CIT (by a very well intentioned controller, i'm sure) whilst still outside its DOC, in which case you can't use it (even if you can recieve it and ident it) untill within range. 20 miles rings a bell, but would be worth checking. I personally had a DME / radial from DTY on my PLOG that put me 18 miles from the CIT, and used that as a fail safe.
Good Luck.
Matty