Cannot set the row property

Hi All,
I have a userform which has a combobox,there is a code like
userform1.initialize
combobox1.rowsource=("pit") 'pit is a range name
end sub
and there is another code like
optionbutton1_click
combobox1.rowsource=("paiza") ' paiza is a range name
end sub
but if that work*** open from web page(still in excel),once I click
optionbutton i generates error.I really could not understand why the
rest of the code is workin but cannot renew the source
property.Everything works fine when I open the *** as a normal excel
file.
Thanks for your help,and please do let me know If I could not explain
clearly.
Regards
baha
.

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