I have a custom object which has lookup fields to Account and Opportunity.  If the Account is populated, instead of using the standard search popup (which shows all opportunities, not just those belonging to the account), I want to use an Opportunity picklist which is populated with the opportunities belonging to the account whenever the account is selected/changed.  I think actionSupport is the right thing to use for this, but I can't get it to work correctly when creating a new record. It works fine in edit mode, when the account is already populated, but when creating a new record, when the search button next to account is used to pick the account, the event is not triggered (first problem).  If I just click in the account field to trigger the OnClick event, it triggers (I can see this in the system log), but the rerender does not happen.  Can anyone explain this?  I'd prefer to invoke actionSupport without having to click in the Account field, but the rerender is the bit giving me the biggest headache.

The page code is as follows:

<apex:page standardController="Call_Meeting_Report__c" extensions="OpportunitySearchController" showHeader="true" sidebar="true">
<apex:form >
<apex:pageBlock title="Call/Meeting Report" mode="edit" id="thePageBlock">
<apex:pageMessages />
<apex:pageBlockButtons >
<apex:commandButton value="Save" action="{!save}"/>
<apex:commandButton value="Cancel" action="{!cancel}" immediate="true"/>
</apex:pageBlockButtons>
<apex:pageBlockSection columns="2">
<apex:inputField value="{!Call_Meeting_Report__c.Account__c}" >
<apex:actionSupport event="onChange" action="{!getOpportunities}" rerender="ChooseOpp" />
<apex:actionSupport event="onkeyup" action="{!getOpportunities}" rerender="ChooseOpp"/>
<apex:actionSupport event="onclick" action="{!getOpportunities}" rerender="ChooseOpp"/>
</apex:inputField>
<apex:pageBlockSectionItem >
<apex:outputPanel id="ChooseOpp">
<apex:outputLabel value="Choose Opportunity"/>
<apex:selectList value="{!Call_Meeting_Report__c.Opportunity__c}" id="opps" size="1">
<apex:selectOptions value="{!Opportunities}"/>
</apex:selectList>
</apex:outputPanel>
</apex:pageBlockSectionItem>
<apex:inputField value="{!Call_Meeting_Report__c.Type__c}"/>
<apex:inputField value="{!Call_Meeting_Report__c.Purpose__c}"/>
<apex:inputField value="{!Call_Meeting_Report__c.Primary_Contact__c}"/>
<apex:inputField value="{!Call_Meeting_Report__c.Other_people_present__c}"/>
<apex:inputField value="{!Call_Meeting_Report__c.Next_actions__c}"/>
<apex:inputField value="!Call_Meeting_Report__c.Date__c}"/>
<apex:inputField value="!Call_Meeting_Report__c.Other_people_present__c}"/>
<apex:inputField value="{!Call_Meeting_Report__c.Discussion__c}"/>
<apex:pageBlockSectionItem />
</apex:pageBlockSection>
</apex:pageBlock>
</apex:form>
</apex:page>

 and the controller is:

public class OpportunitySearchController {

//add an instance variable for the standard controller
private ApexPages.StandardController controller {get; set;}
// the actual call/meeting report
private Call_Meeting_Report__c cmr {get; set;}
private Id a;

public List <selectOption> Opps;

// Initialise the controller
public OpportunitySearchController(ApexPages.StandardController controller) {

//initialise the standard controller
this.controller = controller;
cmr = (Call_Meeting_Report__c)controller.getRecord();
//this.a = (Account)controller.getRecord();

}

// the results from the search
public PageReference getOpportunities() {
Opps = new List<selectOption>();

a = cmr.Account__c;
system.debug('### Account is '+a);
// use some dynamic soql to find the related opportunities by name
try {
List <Opportunity> opplist = [Select o.Id, o.Name from Opportunity o Where AccountId = :a Order By o.Name];
for (Opportunity u:opplist) {
Opps.add(new selectOption(u.Id, u.Name));
system.debug('### option added -'+u.Name);
}
}
catch (Exception e) {
System.debug('### error '+e);
ApexPages.addMessages(e);
}
return null;

}


}

Debug log is showing that the code does get called, but the populated Opportunity pulldown does not appear on the page, which means the rerender isn't happening or I'm doing something else wrong.  Debug log:

18.0 DB,INFO;WORKFLOW,INFO;VALIDATION,INFO;CALLOUT,INFO;APEX_CODE,DEBUG;APEX_PROFILING,INFO
19:08:05.661|CODE_UNIT_STARTED|[EXTERNAL]VForcePage
19:08:05.662|USER_DEBUG|[27,9]|DEBUG|### Account is 001T000000Ga6kPIAR
19:08:05.662|SOQL_EXECUTE_BEGIN|[30,33]|Aggregations:0|Select o.Id, o.Name from Opportunity o Where AccountId = :a Order By o.Name
19:08:05.669|SOQL_EXECUTE_END|[30,33]|Rows:2|Duration:7
19:08:05.670|USER_DEBUG|[34,5]|DEBUG|### option added -Crazy Horses Ltd - Test 1
19:08:05.670|USER_DEBUG|[34,5]|DEBUG|### option added -Crazy Horses Ltd - Test 2
19:08:05.670|CODE_UNIT_FINISHED
19:08:05.672|VF_APEX_CALL|j_id36|{!getOpportunities}|PageReference: none
19:08:05.692|CODE_UNIT_STARTED|[EXTERNAL]VForcePage
19:08:05.692|CODE_UNIT_STARTED|[EXTERNAL]VForcePage
19:08:05.692|USER_DEBUG|[27,9]|DEBUG|### Account is 001T000000Ga6kPIAR
19:08:05.692|SOQL_EXECUTE_BEGIN|[30,33]|Aggregations:0|Select o.Id, o.Name from Opportunity o Where AccountId = :a Order By o.Name
19:08:05.702|SOQL_EXECUTE_END|[30,33]|Rows:2|Duration:10
19:08:05.702|USER_DEBUG|[34,5]|DEBUG|### option added -Crazy Horses Ltd - Test 1
19:08:05.703|USER_DEBUG|[34,5]|DEBUG|### option added -Crazy Horses Ltd - Test 2
19:08:05.703|CODE_UNIT_FINISHED
19:08:05.703|CODE_UNIT_FINISHED

 Any help would be greatly appreciated -

Erica