rich:calendar error msg

[ajaxdev]

when I submit the form, rich:messages shows the following error msg

advertisement:issueDate: '18-11-2009' could not be understood as a date

jsf page:

<h:form>
.....

<rich:calendar
value="#{advertisementAction.issueDate}"
popup="true"
enableManualInput="true"
disabled="false"
monthLabelsShort="true"
showFooter="false"
datePattern="dd-MM-yyyy" />

........

<rich:messages for="issueDate" />


....

<h:commandButton .....
action="#{advertisementAction.insertAdvertisement}" ..../>
....

</h:form>

java bean (AdvertisementAction)

.......
private java.util.Date issueDate;
........

 public java.util.Date getIssueDate() {
 return issueDate;
 }

 public void setIssueDate(java.util.Date issueDate) {
 this.issueDate = issueDate;
 }

please help