# Guide to OpenIG
Chapter 13. Troubleshooting

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## 13.5. Problem accessing URL

    HTTP ERROR 500

    Problem accessing /myURL . Reason:

    java.lang.String cannot be cast to java.util.List
    Caused by:
    java.lang.ClassCastException: java.lang.String cannot be cast to java.util.List
    at org.forgerock.openig.filter.LoggingFilter.writeHeaders(LoggingFilter.java:132
    at org.forgerock.openig.filter.LoggingFilter.logResponse(LoggingFilter.java:119)
    at org.forgerock.openig.filter.LoggingFilter.filter(LoggingFilter.java:86)
    at org.forgerock.openig.filter.Chain.handle(Chain.java:54)

This error is typically encountered when using the AssignmentFilter and setting a string value for one of the Headers. All headers are stored in Lists so the header must be addressed with a subscript. For example, if you try to set `exchange.request.headers['Location']` for a redirect in the response object, you should instead set `exchange.request.headers['Location'][0]`. A header without a subscript leads to the error above.