Server Error, please help.

Hi and if your reading Thank you. This is an error I have never seen before, and its listed below. Its making it to where people try to log on to my server, and it kicks them saying they are already loged in at the time.

Code:

Exception in thread "main" java.lang.NumberFormatException: For input string: "5
3        "
        at java.lang.NumberFormatException.forInputString(Unknown Source)
        at java.lang.Integer.parseInt(Unknown Source)
        at java.lang.Integer.parseInt(Unknown Source)
        at NPCHandler.loadNPCDrops(NPCHandler.java:2277)
        at NPCHandler.<init>(NPCHandler.java:22)
        at server.main(server.java:35)