When trying to upload a file I get the following error message on Safari but not on Firefox. Any help?

TypeError: Result of expression 'form.onsubmit' [null] is not a function.

Chrome gives this error.

TypeError: Property 'onsubmit' of object #<an HTMLFormElement> is not a function

Make sure you're on the latest version of the SWFUpload module.

Now I get this error.

There was a problem with the upload.
The server did not accept it.

It's a PHP error of some sort. Refer to the docs for the steps on troubleshooting SWFUpload responses.

http://doc.silverstripe.org/doku.php?id=modules:swfuploadfield#troubleshooting

It looks like the upload works on small files (~4MB) but not larger files (~11MB).

Yeah, check your upload_max_filesize and max_post_size settings. The lesser of the two will be the ceiling for your uploads. SWFUploadConfig should automatically set the limit to upload_max_filesize.

Where do I edit upload_max_filesize and max_post_size?

I tried the php.ini file and they're set at about 64MB.