The mentioned forum thread is no longer accessible, because it is related to the Upload component, which is part of the discontinued Telerik Extensions for ASP.NET MVC. Here is a concised summary of the information available there.
Basically, the problem is caused by the fact that IE's opacity filter does not work in certain cases. This may be a result of:
Restrictive browser security settings. The IE security setting, which is responsible for making the IE opacity filter work, is "Binary and script behaviors
" and it should be enabled.
A test page, which can be used to find out whether opacity works in general, can be found at: http://jsfiddle.net/9r4xx/3/
The file input, which should be invisible, has a too large font size. Generally, it should have a large font size, but not extremely large. We have found out that 200px is a safe and large-enough value, and this is the value that is set in our stylesheet. Values greater than 220px do not work on all machines and are not recommended.
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