Right now I am using the microsoft mn-500 router. I am haing problems connecting to certain websites. However, when I connect the pc directly to the modem, there are no problems. I reconnect the router and the problems continue. I tried resetting the router and the modem, but no luck.
Go to DslReports and run there tweek test under the tools menu.
It almost sounds like the router has a higher MTU than your pc.
I had the same problem with yahoo mail (delete, attachements ..). Lowereing the MTU on the router to 1400 worked. Then increase to find your max.