2003 Macro is not running fine in 2010 why?

Does it work if you only do a small number of iterations?
if so maybe you just need to clear your history every so often...

Shell "RunDll32.exe InetCpl.cpl,ClearMyTracksByProcess 1"

doing once each 20 a below

myvar = a Mod 20
If myvar = 0 Then
Shell "RunDll32.exe InetCpl.cpl,ClearMyTracksByProcess 1"
Else
End If