To mikrotik experts & ubuntu experts :::> plz help me

[i_hated_microsoft]

my network owner set up Mikrotik Server
i'm a new linux user .. in vista the mikrotik login page easly load when browser open..... but in ubuntu 9.04
when i open firefox i see the title of the login page for a second then disappear and CONNECT FAILD

i ask my friend to help me .. hes old linux user
me and him and network owner spent 5 hours solving this problem
we did evrything .. ports , firewall , browser
evrything ok but the problem still ..
theres ping replying but the browser ...CONNECT FAILD

plz help me
i think ubuntu is fine
but the problem in mikrotik configuration
can anyone tell me . what can i do ??

[i_hated_microsoft]

plz i want help