Not sure if this is a WordPress bug or a Plupload bug, so I thought I'd post it here first to see if other people experience this problem too.
Today one of our clients ran into a problem: file uploads in WordPress (3.4) didn't work (anymore?) in Internet Explorer. I checked and confirmed his problem. The button "select files" exists, but clicking it doesn't do anything. (The "simple" file uploader works fine)
This also happened on another website, but not on two other websites I checked. Other browsers (Opera & Firefox) also work fine.
The two websites that don't work both run on IIS (Windows hosting), the two that do work run on Linux hosting, so I suspect somehow that has something to do with it.
The only thing I could find related to this problem had to do with missing MIME types on the server. I added these MIME types through iirf.ini (the IIS equivalent of .htaccess) and throught the control panel, but to no effect.
Has anyone else experienced this issue?