what i did is , i just added the entity tag section <Entity> ... </Entity> to the customization.xml file.
then imported. so i got the below error details after downloading the file and seeing...
"The import has failed because component new_entityName of type 1 is not declared in the solution file as a root component. To fix this, import again using the XML file that was generated when you exported the solution."
this says the clear thing that we must add the "new_entityName" to the solution.xml file and declare as a root component.
so open the corresponding solution.xml file and search for the "<RootComponents>" tag and add the below with the tags <RootComponents> and </RootComponents>.
<RootComponent type="1" schemaName="new_entityName" />
now zip the files and try to import , it should import smoothly.