buxtooth browser issues - advice please?

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i can't log into buxtooth because they say i have changed my browser. but i'm still on IE the same as yesterday when i did log in. i have recently upgraded ie from 8 to 9, but it's been working for some days. can i have advice on what to do and has anyone encountered this before. also does anyone know why a change of browser would stop you from using a site. seems odd to me. thanks in advance