having trouble sending challenges

everytime i try to challenge someone, a messege comes up saying the page isnt able to be found. Please help, i have to rematches i want to get started on, but nothing is happening and i dont know what to do about it.

i'm not to sure but i had the same problem,it could be to do with your hard drive,my computers 98 and i had the same problem but we have recently got it upgraded to xp and now its fine but there could be a better answer of one of these computer expert's🙂