I have just recently started training my lab to walk with a halti.  She has been doing very very well on it but today I decided to take her round the block and not across the road to the park.  The park in question is past a very busy road.  When I began to turn to walk around the block she stopped dead in her tracks and would not move.  When I tried to coax her with treats etc she still held her ground.  I know she wanted to go to the park but I did not want to go that way today.  I was also frightened that she might slip her halti and run in the road so I didn't know what to do.  In the end I had to turn back and go the way I had come but all the way back she kept on stopping dead behind me and coax as I might with treats etc she would not walk on with me till she was ready.
Is this quite common and is there anything I can do to prevent this becoming a regular occurrence now? 

WHAT?!?! a Labrador refusing to walk...our two will jump round like faries on pitchforks until they get walked! Mabe she just doesnt like the halti, try walking her on something else instead!

Of you use a half check collar (the kind that has a loop of chain attached to a collar) or a 'halti link' (a little loop with trigger hook to attach to halti and collar) to link the headcollar to her normal collar then if the halti comes off you still have the dog attached to the collar.  your dog simply wants to make you go her way, ans I assume you are using the halti to make sure she goes where you say :D

Our Labrador does this sometimes too. He sits on the floor and won't move without a little persuation. He normally wants me to turn around and go back home but I don't let him get his own way. I walk abit further then turn round - or he would do it all the time.

if your dog is not surging ahead and in fact " won't walk "...then you are probably using the wrong tool...put her on a normal collar and take it from there.  Good luck.

We tried a gentle leader, halti and dogmatic with my lab pup - he absolutely hated them all, and was really fed up and depressed.I then used a "walk-eezee" harness - he is much happier with this, and I now use it for getting from A to B, interspersed with short sessions of practising loose lead walking on a normal flat collar. We will get there but it's hard work!

Our Lab does just the same. She is trying to force you to do her will! Having said that she also hates with a passion anything tight round her head face or neck. I walk her on a harness, which has all wide straps, so noting really that exerts any pressure. If she decides to stop, (and she only does this when by herself, with our other dog she is fine) then I walk to the end of the short lead in teh direction that I want to go and stand there until she decides to join me. No pressure on the lead (unless she backs up) but I let it be very much her decision. I do some times coax her to follow, if Im in a hurry but I know from experience that she WILL NOT be forced! So being quitely firm is I have found the only option!