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Its throwing error when you forgot to mention Url.  that’s what I noticed.

IgnoreIfAlreadyExists : True : It will not throw any error if already exists.

IgnoreIfAlreadyExists : False : It throws an error if already exists.

<?xml version="1.0" encoding="utf-8"?>

<Elements xmlns="http://schemas.microsoft.com/sharepoint/">

  <Module Name="MyStyles" Url="Style Library" >

    <File Path="MyStyles\Sample.txt" Url="Sample.txt"  Type="GhostableInLibrary" IgnoreIfAlreadyExists="TRUE" />

    <File Path="MyStyles\NewFolder1\Style.css" Url="NewFolder1/Style.css"  Type="GhostableInLibrary"   IgnoreIfAlreadyExists="TRUE"/>

</Module>

</Elements>