Strangely enough, I can upload files from the Host File Manager and the Upload controls in the HTML module just fine, but the Admin File Manager gives me the following error (in the Event Viewer) when I click the Upload button: 

ModuleId: 396

ModuleDefId: 21

FriendlyName:

ModuleControlSource: DesktopModules/Admin/FileManager/WebUpload.ascx

AssemblyVersion: 7.0.6

PortalID: 0

PortalName: University of Pittsburgh Graduate School of Public Health

UserID: 1

UserName: upph_host

ActiveTabID: 73

ActiveTabName: File Manager

RawURL: /admin/file-manager/ctl/edit/mid/396/ftype/file/rtab/73

AbsoluteURL: /Default.aspx

AbsoluteURLReferrer: http://upphv7.dev.pipitonegroup.com/admin/file-manager

UserAgent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:21.0) Gecko/20100101 Firefox/21.0

DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke

ExceptionGUID: a6b0171e-f4df-46d1-b125-e1ab8e5e4eb1

InnerException: Requested value 'file' was not found.

FileName:

FileLineNumber: 0

FileColumnNumber: 0

Method: System.Enum.TryParseEnum

StackTrace:

Message: DotNetNuke.Services.Exceptions.ModuleLoadException: Requested value 'file' was not found. ---> System.ArgumentException: Requested value 'file' was not found. at System.Enum.TryParseEnum(Type enumType, String value, Boolean ignoreCase, EnumResult& parseResult) at System.Enum.Parse(Type enumType, String value, Boolean ignoreCase) at DotNetNuke.Modules.Admin.FileManager.WebUpload.get_FileType() at DotNetNuke.Modules.Admin.FileManager.WebUpload.OnLoad(EventArgs e) --- End of inner exception stack trace ---

Source:

Server Name: VOYAGER

Possibly important: I am using ifinity URL Master.

Confirmed. If I uncheck the "Do 301 redirect when Url is not in Lower Case?" checkbox (under Host > Friendly URL Settings > Advanced Settings), then the Admin File Manager's upload functionality functions normally. Thankfully, I was at least able to leave the "Change all Urls in the site to be lower case" checked and it works fine. 

I find it kind of disappointing that a major function would be case-sensitive like that. :|