IIS 7 has a default upload limit if 30,000,000 bytes which is about 28.61 MB. When the setting in SharePoint is increased to say 100MB upload size, you still cannot upload files greater than the 28MB. How do you fix it? You can either install the IIS Administration Pack or modify the following file: C:\Windows\System32\inetsrv\config\applicationHost.config
You would add the following to the <requestFiltering> section
<requestLimits maxAllowedContentLength=”[length in bytes]” />
So for 100MB you would enter 104857600. It would be wise to make this a little larger than what you are setting in SharePoint for some wiggle room. This should allow you to upload files that are larger than the default 28.61MB.