I removed all existing cookies, disabled javascript and cookies in firefox prior to logging in, and was still able to successfully log in, so it doesn't look like javascript or cookie issue (even though the site does set a cookie per HTTP Watch).

I changed the structure of my form submission to this:

    $mech->submit_form(
        form_name => 'HashForm1',
        fields => {
            login_password => 'username',
            login_username => 'password',
            prefLanguage => '00000000',

        },
        button => "submit",
    );
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$mech->form_name('HashForm1');
$mech->field("login_username",'username');
$mech->field("login_password",'password');
$mech->field("prefLanguage",00000000);
$mech->submit_form();
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Thanks for the help so far, everyone. I'm looking into HTTP:Recorder right now, and I'm feeling like I'm moving at least a little toward a solution at this point.

Are you sure that your submit button is named "submit"? Yes, the code is different (you're now sending button info too).

I recommend you to use LiveHttpHeaders for Firefox and make exactly same request with $mech->post()

Thanks.
Roman

I'm using HTTP Watch through IE (I'm somewhat limited in what I can use in my corporate enviornment) to capture the data from the form submission -- I assume that HTTP Watch will capture the same data as LiveHttpHeaders. Here is the post data as captured by HTTP Watch:

paramater       value           size
login_password    passoword    18    
login_username    username    18    
prefLanguage    00000000    21    
submit        Log On            13
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and here is the only cookie (which doesn't seem necessary since I can log in with cookies turned off)

Name    Direction Value Path    Domain          Duration   
C0    Sent      apc    /    .192.168.0.2    (Session)

HTTP Only    Secure 
No         Yes
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and, finally, here is the header information

Header Sent                                      Value
(Request-Line)    POST /Forms/login1 HTTP/1.1
Accept    application/x-ms-application, image/jpeg, application/xaml+x
+ml, image/gif, image/pjpeg, application/x-ms-xbap, application/vnd.ms
+-excel, application/vnd.ms-powerpoint, application/msword, */*
Accept-Encoding    gzip, deflate
Accept-Language    en-US
Cache-Control    no-cache
Connection    Keep-Alive
Content-Length    73
Content-Type    application/x-www-form-urlencoded
Cookie    C0=apc
Host    192.168.0.2
Referer    https://192.168.0.2/logon.htm
User-Agent    Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64
+; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CL
+R 3.0.30729; .NET4.0C; MS-RTC LM 8; InfoPath.2)
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