Uploading Documents requires Active X Control so I would recommend you to use Internet Explorer with Active X control installed.
The Active X control used for the multi document upload does not exist in a 64-bit version.
The 64-bit Office version also does not include the 32-bit version of the active x controls.
That's why it is recommend to use the 32-bit version of Office in combination with SharePoint.
or if you can use sharepoint workspace then follow these steps
Upload files to SharePoint Workspace, and sync it to site.
a. Log on to SharePoint Team site, then click "Site Actions" -> "Sync to SharePoint Workspace". The content in site will be synced to
b. Choose the folder which one you want to be uploaded document, then
click "Add document" to upload the .wav file.
c. Click the option "Sync"->"Sync Workspace" in the top ribbon, all
changed in Workspace will be synced to SharePoint site.
Open files in explorer, and then copy the .wav file to it. Click
Library Tools->Library, choose the option "Open with Explorer".
Check this link out, guy has same problem as you
Problem uploading documents
Hope this helped :)