This is one of the errors you get when you are trying to import your Data in AX 2012 through the Data Import Export Framework.
It is very frustrating to trace that one record, from a large set of data that is the cause of this error. This error usually arises when your primary key is duplicated in the import data file.
Always make sure to perform the following steps before importing your Data in AX 2012 through the Data Import Export Framework. Open your file in excel and select the primary key column. Go to Condition Formatting in the Home tab and select Highlight Cell Rules-> Duplicate Values. This function will highlight the duplicated primary key records. Fix the records before importing your data in AX in order to avoid such errors.