"Can't make "documents" into type integer." -1700
The joys of variable typing in AppleScript. I think that your problem is in the line 

set fullKindlePath to POSIX path of (kindleLocation as alias) &amp; "documents"


I would try changing this to 

set fullKindlePath to (the POSIX path of (kindleLocation as alias)) &amp; "documents"


then if that doesn't work try &amp; ("documents" as POSIX PATH)

By the way, are you sure that fullKindlePath has a '/' at the end?