Problem With IE And (ajax) File Upload Via Iframe: Javascript Error Access Denied/zugriff Verweigert

i want to do (multiple) file upload(s) and display a progress bar.
with firefox and safari it is no problem at all. only IE makes some
problems.

my script is based on ajax-uploader, which can be found at
www.srmiles.com/freestuff/ajax_file_uploader/ . you can do multiple
file uploads. each upload will have it's own "form"-tag, so that each
file is uploaded for its own. could be a good solution if there are
"big" uploads.

so here is what i do:

i have a html-page in which several forms with file-input fields are
generated. when i now hit the "one" submit button at the bottom of the
page a javascript function upload() starts it will iterate through all
forms (id='frmUpload_xx'), will get the filename, start a ajax request
for the progress-bar function and do a form.submit().

if the first form/file is uploaded, a settimeout('upload()', 1000); is
called and the next form will be processed. all form's have an
target="uploaddiv", where uploaddiv is a invisible iframe. so the
output of the upload script is put in this div. output should only be
a "OK" at the end. no usefull output no info no nothing.

firefox and safari are working as expected, only IE stops after the
first file is uploaded. i get an javascript error saying "zugriff
verweigert/access denied" on object line x... this is the place where
i call "form.submit()".

this is the upload-function:

function upload() {
if (uploads.length>0) {
form = document.getElementById('frmUpload_'+uploads[0]);
if (form["filename"].value == ""){
alert("Please Choose a file to upload.");
} else {
filename = form["filename"].value;
if (filename.lastIndexOf("")>0) {
filename = filename.substring(filename.lastIndexOf("")
+1,filename.length);
} else if (filename.lastIndexOf("/")>0) {
filename = filename.substring(filename.lastIndexOf("/")
+1,filename.length);
}
makeRequest("upload_progress.php?sid="+sid
+"&filename="+filename,progress);
form.submit();
}
}
}

the strange thing is, that filename is filled correct, that means the
object "form" is found and exisits. the first iteration is working,
only the second ends with an error.

think it have something to do with redirecting the output of the
upload-script in an iframe. after that IE can't access form - at least
IE is not allowed to submit the form as i can access a form field
(filename).
i worked on that the last two days and haven't found a solution...