Mac Sierra - Batch Convert Pages to Plain Text
This script works for me, tested on MacOS Sierra and Pages Version 6.0.5

set mfolder to "Macintosh HD:Users:me:Documents:convertme:"
set destFolder to "Macintosh HD:Users:me:Documents:converted:"

tell application "Finder" to set theNames to name of files of folder mfolder

tell application "Pages"
    repeat with aName in theNames
        set theDoc to open ((mfolder &amp; aName) as alias)
        set newFile to destFolder &amp; (text 1 thru -7 of aName) &amp; ".txt" -- concat destFolder and the name without the ".pages" extension 
        my makenewFile(newFile)

        export theDoc to file newFile as unformatted text
        close theDoc
    end repeat
end tell

on makenewFile(thePath)
    close access (open for access thePath)
    -- delay 0.5 -- use the delay command, If you still have a permission issue,  increase the number of seconds
end makenewFile