How can I programmatically click on an image button to submit a form

Hi Experts,

I am using the IE web browser object in a MS Access form to automatically log into my online telephone account, although I am having a problem submitting the form.  I am using the following visual basic code:

    WebBrowserCallagenix.navigate "http://www.callagenix.com/"
    DoEvents: DoEvents: DoEvents
    Do While WebBrowserCallagenix.Busy   'wait until the page loads by looping
      DoEvents
    Loop
    Set doc = WebBrowserCallagenix.Document    'access the document properties
    DoEvents
    Do While WebBrowserCallagenix.Busy
        DoEvents
    Loop  
    returnValue = FillForm("pAccountCode", "my_account", False)
    returnValue = FillForm("pPassword", "my_password", False)
    WebBrowserCallagenix.Document.Forms("cgxlogin").submit

The above code enters the account name and password into the appropriate fields but I then receive the following error message:
 'Object doesn't support this property or method'

I think the issue is to do with the fact that the form uses the post method and/or an image for the login button, but this doesn't help me figure out how to submit the form.

Any ideas?

Here is the html code for the form itself:

<form name="cgxlogin" target="_top" id="cgxlogin" method="post" action="https://secure.callagenix.com/Pages/login/login.asp">
<label for="Account">Account</label><br />                    
<input name="pAccountCode" type="text" class="formfieldreg" id="pAccountCode" size="10" maxlength="10" />
<br />
<label for="Password">Password</label><br />                    
<input name="pPassword" type="password" class="formfieldreg" id="pPassword" size="10" maxlength="10" />
<input type="hidden" name="Submit" value="Login" />
<input name="imageField" type="image" id="login-button" src="images/new/button-login.gif" alt="Login" />
<a href="/registration/register.asp" title="Create New Account"><img src="images/new/button-reg.gif" alt="Register" width="76" height="26" border="0" /></a>
</form>

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