Data Transfer Workbench - Price list could not be found error.

Dear All, i am trying to update prices in my SBO using Data Transfer Workbench Tool. "ItemsList" text file has 8500 items in it, "PriceList" text file has 17000 lines (each item has 2 prices). I wasted the whole day yesterday trying to figure out what was wrong with my source files, but found nothing. Every time i run update using DTW I get "Price list could not be found error". What is interesting is that DTW imports/updates number of records and after that failes. The number of successfully updated records changes everytime i run DTW. Please advice.