The same thing happens to me on and off (has been for a couple of years). The ISAPI.dll is from eBay, some form of script, I expect, that usually automatically downloads when accessing certain pages (you will find it's actually in the URL of My eBay pages and some others if you check the address at the top). So it's not a virus or keylogger.
Every now and then, though, my browser (both Firefox and Chrome) prompts me to download it to my computer before opening the page. I always click cancel then refresh, and the page loads as normal.
