Adding a large amount of new inventory

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We are adding a large number of new products to our Inventory Master list which requires new part numbers, adding each part to the Pricing list, entering the quantities for each part and its location.  What is the most efficient method to add this information?  I have attempted to create an Excel spreadsheet to import the data (4 different times into 4 different screens for the different tasks) but I keep getting an error message stating "The Microsoft Access database engine cannot open or write to the file ".  It is already opened exclusively by another user, or you need permission to view and write its data."

What am I missing in order to get these files ready to upload?

Thanks,

Lisa