Can somebody help me this error. Unable to figure out where is the mistake.
While this isn't an answer to your question, do you want to try posting this in https://community.anaplan.com/t5/API-Developers/gh-p/DevelopersGroup (API Developers group) also, to see if someone can address this?
For me it looks like path to the file you want to upload as part of this import (argument FilePath) is incorrect - it doesn't have file extension at the end (probably ".csv"). To always ensure that you provide right path to the filename, I advise you to find your file in File Explorer, hold Shift and mouse right click - it will open context menu and one of the options will be "Copy as path". Choose it and then paste it in your script.
Also, validate if FileName argument is the same as in Anaplan - I see that you use CSV, and if you haven't renamed your source file, it should also have extension, like "test import.csv".
It looks like a line below the "*** End of settings - Do not edit below this line ***" comment has been changed. It should be just
set Command=.\AnaplanClient.bat %Credentials% %Operation%