I Just re-ran the instlalation and got the same error message. There was indeed a log created text as below:-
********* FSUIPC, Version 3.989u by Pete Dowson *********
Running on Windows Version 5.1 Build 2600
Verifying Certificate for "F:\Program Files\Microsoft Games\Flight Simulator 9\MODULES\FSUIPC.dll" now ...
SUCCESS! Signature verifies okay!
Running inside FS2004 (FS9.1 CONTROLS.DLL, FS9.1 WEATHER.DLL)
User Name="nicholas weber"
User Addr="nicholas_weber@libero.it"
FSUIPC Key is provided
WIDEFS not user registered, or expired
Module base=61000000
WeatherReadInterval=4
LogOptions=00000001
DebugStatus=15
2656 System time = 27/01/2013 11:29:15
2656 F:\Program Files\Microsoft Games\Flight Simulator 9\
2672 System time = 27/01/2013 11:29:15, FS2004 time = 12:00:00 (00:00Z)
4094 C:\Documents and Settings\Laura Tesoro.ALBERT\My Documents\Flight Simulator Files\lev.flt
4203 AIRCRAFT\Vickers Super VC10\VC105.air
4219 Aircraft="Vickers Super VC10 BOAC"
11703 ERROR: Can't change message filter: functions not available
12187 Advanced Weather Interface Enabled
14062 C:\Documents and Settings\Laura Tesoro.ALBERT\My Documents\Flight Simulator Files\UI generated flight.flt
14609 Clear All Weather requested: external weather discarded
45047 Traffic File #17 = "scenery\world\scenery\traffic030528"
46484 Traffic File #38 = "scenery\world\scenery\traffic_eur"
47266 Traffic File #25 = "scenery\world\scenery\traffic_bucaresti"
47531 Traffic File #44 = "scenery\world\scenery\traffic_moncook"
47672 Traffic File #31 = "scenery\world\scenery\traffic_cuneo"
47781 Traffic File #39 = "scenery\world\scenery\traffic_fiumi"
63031 WeatherOptions set, now 681C378B (timer=0)
64203 Traffic File #19 = "scenery\world\scenery\traffic_airone"
64547 Traffic File #28 = "scenery\world\scenery\traffic_caselle"
65891 Traffic File #47 = "scenery\world\scenery\traffic_stanstead"
66000 Traffic File #49 = "scenery\world\scenery\traffic_tom"
66937 Traffic File #21 = "scenery\world\scenery\traffic_bahrain"
67047 Traffic File #30 = "scenery\world\scenery\traffic_china"
5200234 System time = 27/01/2013 12:55:52, FS2004 time = 11:29:26 (10:29Z)
5200234 *** FSUIPC log file being closed
Memory managed: 0 Allocs, 38171 Freed
********* FSUIPC Log file closed ***********
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vololiberista