File upload fails randomly with following exception:

2008-06-13 14:53:40,075 ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[localhost].[/inputFile].[uploadServlet]] Servlet.service() for servlet uploadServlet threw exception
javax.faces.el.EvaluationException: javax.el.PropertyNotFoundException: Target Unreachable, identifier 'inputFile' resolved to null
at com.sun.faces.application.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:84)
at com.icesoft.faces.component.inputfile.InputFile.setProgress(InputFile.java:866)
at com.icesoft.faces.webapp.http.core.UploadServer$ProgressCalculator.potentiallyNotify(UploadServer.java:167)
at com.icesoft.faces.webapp.http.core.UploadServer$ProgressCalculator.setListenerAndContextAndPFS(UploadServer.java:143)
at com.icesoft.faces.webapp.http.core.UploadServer$2.servlet(UploadServer.java:70)
at com.icesoft.faces.webapp.http.servlet.ServletRequestResponse.detectEnvironment(ServletRequestResponse.java:222)

Caused by: javax.el.PropertyNotFoundException: Target Unreachable, identifier 'inputFile' resolved to null
at org.apache.el.parser.AstValue.getTarget(AstValue.java:46)
at org.apache.el.parser.AstValue.invoke(AstValue.java:127)
at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:276)
at com.sun.faces.application.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:77)