Application_AuthenticateRequest execute 4 times

[Tony]

Hi,
I've never seen similar problem before.
Application_AuthenticateRequest in Global.asax.vb file
execute 4 time before it exit to the default.vb file.
Plus, in every run, the code execution jump back to the
previous line that already been executed (I'll explain):

example :
line 1 : Sub Application_AuthenticateRequest( ....)
line 2: If (a=b) Then
line 3: a=c
line 4: End IF
line 5: ...
line 20: End Sub

the code execution run in the following direction:
line1 then line2 , then line1 again, then line2 again.
line 3 then line4, then line 3 again, then line4
again, .......
and it keep running this way until "End Sub".

any help would be really appreciated.