I am unable to render outputPanel based on the picklist Value selection. Please let me know what is wrong with my code.
Thanks in advancve!!
 

<apex:page standardController="Case" extensions="PublisherController" showHeader="false">
<apex:form >
    <br/><br/><br/><br/>
    <table align="center" width="50%" cellpadding="5">
        <tr>
            <th></th>
            <th></th>
            <th></th>
            <th></th>
        </tr>
        <tr>
            <td align="right"><apex:outputText >Model</apex:outputText>
            </td> 
            <td align="left"><apex:inputField value="{!case.Model__c}"/>
            </td>
            <td align="right" rowspan="2"><apex:outputText >Description</apex:outputText>
            </td>
            <td align="left" rowspan="2"><apex:inputField value="{!case.description}"/>
            </td>
        </tr>
        <tr>
            <td align="right"><apex:outputText >Category</apex:outputText>
            </td> 
            <td align="left"><apex:inputField value="{!case.Category__c}"/>
            </td>
            <td align="right">
            </td>
            <td align="center">
            </td>
        </tr>
        <tr>
            <td align="right"><apex:outputText >Problem</apex:outputText>
            </td> 
            <td align="left">
                <apex:ModelRegion >
                    <apex:inputField value="{!case.Problem__c}"><apex:ModelSupport event="onchange" reRender="ddc"/></apex:inputField>
                </apex:ModelRegion>
            </td>
            <apex:outputPanel rendered="{!case.Problem__c=='Repair'}" id="ddc">
                <td align="right"><apex:outputText >Requested Day</apex:outputText>
                </td>
                <td align="left"><apex:inputField value="{!case.Requested_Date__c}"/>
                </td>
            </apex:outputPanel>
        </tr>
        <tr>
            <td align="right">
            </td> 
            <td align="right"><apex:commandButton value="Cancel" Model="{!Cancel}"/>
            </td>
            <td align="left"><apex:commandButton value="Create Case" Model="{!save}"/>
            </td>
            <td align="center">
            </td>
        </tr>
    </table>
</apex:form>
</apex:page>