This is occurring because not all browsers - like IE8 and IE9 - support RGBa. Try writing a "backup" using RGB for all properties containing RGBa. RGB does not include transparency but it is supported by most older browsers. Here is an example:
background-color: rgb(102, 102, 102);
background-color: rgba(255, 255, 255, 0.05);
The first property will be read if the browser does not support RGBa. Don't for get to check all CSS elements in the CSS editor that are using RGBa and apply a RGB backup.
Please let me know if anything is unclear.