Internet streaming radio won't work?

A couple of weeks ago I was able to access a radio stations internet stream on my office computer, but now it will not connect. I have tried WMP, Real Player and iTunes. The weird part is I can go through a sister station's website and access the same morning shows stream perfectly well. I thought it was the original site having network problems, but it isn't because I can listen at home perfectly fine. So my question is why can I listen to some internet streaming radio on my office computer but not others?