this problem occured in josm, any ideas_?

PUT http://api.openstreetmap.org/api/0.6/changeset/create... OK
POST http://api.openstreetmap.org/api/0.6/changeset/4770655/upload... Bad Request
Error header: Placeholder node not found for reference -56832 in way -56831
org.openstreetmap.josm.io.OsmApiException: ResponseCode=400, Error Header=
at org.openstreetmap.josm.io.OsmApi.sendRequest(OsmApi.java:622)
at org.openstreetmap.josm.io.OsmApi.sendRequest(OsmApi.java:505)
at org.openstreetmap.josm.io.OsmApi.uploadDiff(OsmApi.java:455)
at org.openstreetmap.josm.io.OsmServerWriter.uploadChangesInChunks(OsmServerWriter.java:163)
at org.openstreetmap.josm.io.OsmServerWriter.uploadOsm(OsmServerWriter.java:205)
at org.openstreetmap.josm.gui.io.UploadPrimitivesTask.realRun(UploadPrimitivesTask.java:237)
at org.openstreetmap.josm.gui.PleaseWaitRunnable.doRealRun(PleaseWaitRunnable.java:83)
at org.openstreetmap.josm.gui.PleaseWaitRunnable.run(PleaseWaitRunnable.java:129)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:636)