cannot move an user to another group

[steph@ne]

I want to move a user from a group to another group but it does nothing.
I have these trace in the log file

Sep 15, 2011 11:47:12 AM com.openexchange.ajax.Group doPut
SEVERE: SVL-0001 Category=8 Message=Exception while writing JSON. exceptionID=1666531341-42431
SVL-0001 Category=8 Message=Exception while writing JSON. exceptionID=1666531341-42431
        at com.openexchange.ajax.Group.doPut(Group.java:165)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:619)
        at com.openexchange.ajax.AJAXServlet.service(AJAXServlet.java:392)
        at com.openexchange.ajax.SessionServlet.service(SessionServlet.java:174)
        at com.openexchange.ajax.PermissionServlet.service(PermissionServlet.java:66)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
        at com.openexchange.ajp13.najp.AJPv13RequestHandlerImpl.doServletService(AJPv13RequestHandlerImpl.java:504)
        at com.openexchange.ajp13.AJPv13Request.response(AJPv13Request.java:129)
        at com.openexchange.ajp13.najp.AJPv13RequestHandlerImpl.createResponse(AJPv13RequestHandlerImpl.java:316)
        at com.openexchange.ajp13.najp.AJPv13ConnectionImpl.createResponse(AJPv13ConnectionImpl.java:207)
        at com.openexchange.ajp13.najp.AJPv13Task.call(AJPv13Task.java:346)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:269)
        at java.util.concurrent.FutureTask.run(FutureTask.java:123)
        at com.openexchange.threadpool.internal.CustomThreadPoolExecutor$Worker.runTask(CustomThreadPoolExecutor.java:738)
        at com.openexchange.threadpool.internal.CustomThreadPoolExecutor$Worker.run(CustomThreadPoolExecutor.java:764)
        at java.lang.Thread.run(Thread.java:595)
Caused by: org.json.JSONException: JSONArray[26] is not a number.
        at org.json.JSONArray.getDouble(JSONArray.java:192)
        at org.json.JSONArray.getInt(JSONArray.java:206)
        at com.openexchange.ajax.parser.GroupParser.parseMember(GroupParser.java:92)
        at com.openexchange.ajax.parser.GroupParser.parse(GroupParser.java:84)
        at com.openexchange.group.servlet.request.GroupManageRequest.actionUpdate(GroupManageRequest.java:165)
        at com.openexchange.group.servlet.request.GroupManageRequest.performAction(GroupManageRequest.java:128)
        at com.openexchange.ajax.request.GroupRequest.action(GroupRequest.java:118)
        at com.openexchange.ajax.Group.doPut(Group.java:153)
        ... 15 more

How to fix it ?
thanks for your answers

[steph@ne]

It seems that the issue occurs when the users is the last one of the list
hope it helps

[Martin Heiland]

hi,

what command do you exactly use to "move" users between groups? What OX version are you using?

Greetings