Sometimes the dip tubes have little protrusions on them that go into matching slots on the ID of the keg fitting. Try rotating the tube back and forth to make the features mate. You might have to reach into the keg to be able to rotate the dip tube.
AHA! This was it. The top of the dip tube had tiny little indents that went along with the keg insert, alligning that plus I used some petrol lube did it.
Thanks so much to everyone here. Cheers.