CKFinder button text problem

I have purchased and installed CKFinder for a client's Content Management System. When I upload a document or image to the site, the buttons are styled correctly and I can read the text. When my client tries to upload a document to the same site, the buttons appear light grey with white text and she cannot read their labels.

You can see this in the attached screenshot. The top image is her view and the bottom is my view of the same page.

It looks like a styles issue to me but I'm stumped about why it looks fine for her but not for me. I've viewed it in both IE and Firefox. My client is using the same version of IE as me and we are viewing the same site but with different results. It makes the control unusable for her.

Does anyone have any suggestions?

Thanks in advance!

Sas