When using multiple file upload if you are facing problem of Some of client computers shows Drag and Drop feature and some of are not ,you like this article. First of all Multiple File upload is not a sharepoint feature.It is a Microsoft Office feature and working with just only IE8(+) and Office installed machines.This feature is not supported by other browsers like firefox and chrome. Sharepoint provide an ActiveX control named “STSupld.UploadCtl” via interacting with Microsoft Office’s dll of STSUPLD.DLL at background. And the version of this dll is define that you have Drag and Drop option or not. we e.g see that ActiveX control and there isnt any Silverlight in this issue.
More clearly if your client computer have installed Office 2010 than you have drag drop option if only have office 2007/2003 installed than you see old version of dialog with CheckBoxes. There isn’t any way to use this option on office 2007 installed computers except installing or upgrading office 2010 according to Microsoft Licence agreements .
Sometimes we are getting problem with this feature even if we are using that Office 2010. The possible problem is here the old version of dll still remain in background. You can able to check the activeX control dll from your IE -> Tools -> “Manage Add ons”
The versions below show us which office is in use.
11.0.xxxx Office 2003
12.0.xxxx Office 2007
14.0.xxxx Office 2010
Also you can find the assemblies defined folders
C:\Program Files (x86)\Microsoft Office\Office14\STSUPLD.DLL
C:\Program Files (x86)\Microsoft Office\Office12\STSUPLD.DLL
C:\Program Files (x86)\Microsoft Office\Office11\STSUPLD.DLL
If you somehow remove or currupt this dll you could not be use Multiple File Upload feature anymore.