No - obviously there are many variables in a case, but it's not the end of the world. Depends on the level of help - I.e did you not know the revenue formula or was it to do with the structure of pharma and its drivers?
I've heard of people really getting suck, getting help with maths (either cant work out the logic or getting the calc wrong), overlooking things all together and still passing the case.
People make mistakes and get stuck, we are all human. If you are 90% of the way there, or if you are generally fairly excellent, structured, controlled and enthusiastic about the process, it's likely getting a little nudge from the case interviewer will be fine.
This is why its so important to bring the interviewer along on the case with you, solve it 'together' and they will want to help you. Consultants get stuck all the time on cases, they leverage their team and network to overcome problems...I don't believe 1 person can solve every aspect of every case to the full standard and 100% accuracy.
If you do get stuck, acknowledge this, take a step back, digest the new info, relate to the objective of the case and just move on. Dont let this bother you - One area being indirectly assessed is the ability to recover from mistakes and act under pressure.
Hope this helps.