Huge Discrepancy in Data

I am facing a major issue between the number of clicks being recorded on AdWords Vs. the number of Visits being recorded on Omniture. 

I know for a fact that there will always be a minor discrepancy in data because during the same visit, a user might have clicked on the Ad more than once. However, I am facing a major discrepancy in data where for instance when AdWords has recorded 377,000 clicks, only 90,000 visits are being recorded on Omniture. 

This is causing a lot of trouble from the client's side because they feel that we are not driving enough traffic. All my campaigns are tagged properly, and I can even see them from the tracking code section on Omniture. 

Please advise.