Retrying and suspending an activty in status monitor gives error on page

I am trying to retry a workflow activity in status monitor logged in as sysadmin and every time i try restart or cancel a workflow i alwasys get this error as shown below.

although to the activity does starts or stops when ever i do this but i have close the current window and log in again to view the results.

what should i do to stop seeing this error.

oracle.apps.fnd.framework.OAException: java.lang.NullPointerException at oracle.apps.fnd.framework.OAException.wrapperException(OAException.java:912) at oracle.apps.fnd.framework.webui.OAWebBeanHelper.processRequest(OAWebBeanHelper.java:647) at oracle.apps.fnd.framework.webui.OAWebBeanContainerHelper.processRequest(OAWebBeanContainerHelper.java:267) at oracle.apps.fnd.framework.webui.beans.layout.OAFlowLayoutBean.processRequest(OAFlowLayoutBean.java:353) at oracle.apps.fnd.framework.webui.OAWebBeanHelper.processRequestChildren(OAWebBeanHelper.java:1003) at oracle.apps.fnd.framework.webui.OAWebBeanHelper.processRequestChildren(OAWebBeanHelper.java:970) at oracle.apps.fnd.framework.webui.OAWebBeanHelper.processRequest(OAWebBeanHelper.java:690) at oracle.apps.fnd.framework.webui.OAWebBeanContainerHelper.processRequest(OAWebBeanContainerHelper.java:267) at oracle.apps.fnd.framework.webui.beans.layout.OAStackLayoutBean.processRequest(Unknown Source) at oracle.apps.fnd.framework.webui.OAWebBeanHelper.processRequestChildren(OAWebBeanHelper.java:1003) at oracle.apps.fnd.framework.webui.OAWebBeanHelper.processRequestChildren(OAWebBeanHelper.java:970) at oracle.apps.fnd.framework.webui.OAWebBeanHelper.processRequest(OAWebBeanHelper.java:690) at oracle.apps.fnd.framework.webui.OAWebBeanContainerHelper.processRequest(OAWebBeanContainerHelper.java:267) at oracle.apps.fnd.framework.webui.beans.layout.OAFlowLayoutBean.processRequest(OAFlowLayoutBean.java:353) at oracle.apps.fnd.framework.webui.OAWebBeanHelper.processRequestChildren(OAWebBeanHelper.java:1003) at oracle.apps.fnd.framework.webui.OAWebBeanHelper.processRequestChildren(OAWebBeanHelper.java:970) at oracle.apps.fnd.framework.webui.OAWebBeanHelper.processRequest(OAWebBeanHelper.java:690) at oracle.apps.fnd.framework.webui.OAWebBeanContainerHelper.processRequest(OAWebBeanContainerHelper.java:267) at oracle.apps.fnd.framework.webui.beans.form.OAFormBean.processRequest(Unknown Source) at oracle.apps.fnd.framework.webui.OAWebBeanHelper.processRequestChildren(OAWebBeanHelper.java:1003) at oracle.apps.fnd.framework.webui.OAWebBeanHelper.processRequestChildren(OAWebBeanHelper.java:970) at oracle.apps.fnd.framework.webui.OAWebBeanHelper.processRequest(OAWebBeanHelper.java:690) at oracle.apps.fnd.framework.webui.OAWebBeanContainerHelper.processRequest(OAWebBeanContainerHelper.java:267) at oracle.apps.fnd.framework.webui.beans.OABodyBean.processRequest(OABodyBean.java:353) at oracle.apps.fnd.framework.webui.OAPageBean.processRequest(OAPageBean.java:2771) at oracle.apps.fnd.framework.webui.OAPageBean.preparePage(OAPageBean.java:1991) at oracle.apps.fnd.framework.webui.OAPageBean.preparePage(OAPageBean.java:567) at oracle.apps.fnd.framework.webui.OAPageBean.preparePage(OAPageBean.java:455) at _pages.__oa._jspService(__oa.java:233) at weblogic.servlet.jsp.JspBase.service(JspBase.java:34) at weblogic.servlet.internal.StubSecurityHelper$ServletServiceAction.run(StubSecurityHelper.java:227) at weblogic.servlet.internal.StubSecurityHelper.invokeServlet(StubSecurityHelper.java:125) at weblogic.servlet.internal.ServletStubImpl.execute(ServletStubImpl.java:301) at weblogic.servlet.internal.TailFilter.doFilter(TailFilter.java:26) at weblogic.servlet.internal.FilterChainImpl.doFilter(FilterChainImpl.java:60) at oracle.apps.fnd.security.WLFilter.doFilter(WLFilter.java:213) at weblogic.servlet.internal.FilterChainImpl.doFilter(FilterChainImpl.java:60) at oracle.apps.jtf.cabo.interceptor.JTFWrapperFilter.doFilter(JTFWrapperFilter.java:141) at weblogic.servlet.internal.FilterChainImpl.doFilter(FilterChainImpl.java:60) at oracle.apps.jtf.base.session.ReleaseResFilter.doFilter(Unknown Source) at weblogic.servlet.internal.FilterChainImpl.doFilter(FilterChainImpl.java:60) at oracle.apps.fnd.security.AppsServletFilter.doFilter(AppsServletFilter.java:432) at weblogic.servlet.internal.FilterChainImpl.doFilter(FilterChainImpl.java:60) at oracle.security.jps.ee.http.JpsAbsFilter$1.run(JpsAbsFilter.java:119) at java.security.AccessController.doPrivileged(Native Method) at oracle.security.jps.util.JpsSubject.doAsPrivileged(JpsSubject.java:315) at oracle.security.jps.ee.util.JpsPlatformUtil.runJaasMode(JpsPlatformUtil.java:442)