Missing exact steps to reproduce: «When I was attempting to upload 5 files at once, all having different sources and license information, after providing their descriptions, there are two types of error messages which I get, and the upload does not continue (with Internet Explorer 9)».
https://commons.wikimedia.org/w/index.php?title=Commons:Upload_Wizard_feedback&oldid=106815121#Upload_wizard_not_working_when_I_upload_5_files_at_once_with_each_one_having_a_different_license

Errors:

Webpage error details

User Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; .NET4.0E)
Timestamp: Wed, 19 Sep 2012 12:26:52 UTC

Message: Object doesn't support property or method 'toLowerCase'
Line: 10
Char: 281
Code: 0
URI: http://bits.wikimedia.org/commons.wikimedia.org/load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=20120912T175701Z

Message: Object doesn't support property or method 'toLowerCase'
Line: 67
Char: 304
Code: 0
URI: http://commons.wikimedia.org/wiki/Special:UploadWizard

Version: master
Severity: normal