hi,
you need an Excel file containing XML fileds mapping (generated from RapidStart and embedded in Excel file); if your source system overwrite the file, your structure is lost and you receive error message.
(you can only fill the excel sheet created from Rapid Start and then import the excel sheet)
some links:
Set Up a Company With RapidStart Services for Microsoft Dynamics NAV
msdn.microsoft.com/.../hh179428(v=nav.71).aspx
Tips and Tricks: RapidStart Services
msdn.microsoft.com/.../hh879494(v=nav.71).aspx
Rapid Start Config
RapidStart Services: Configuration Worksheet
www.mibuso.com/.../viewtopic.php
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you can try these others solutions:
NAV 2013 Universal XMLPort v5
Excel Import Export Wizard - NAV 2013
or Import external data using NAV Web Services Technology (with XMLPorts)